I was wondering what might lead some countries to have very short T-lists (1-2 sites). The reasons can be diverse. Some countries simply cannot offer that much (Luxemburg, Barbados, Qatar etc.) which is fine. Other countries might have problems tracking possible candidates or preparing their nominations. Others yet just find themselves already well represented.
Here's a list of such countries. Any interesting insights regarding them?

Australia (2)
Belize (0)
Costa Rica (2)
Eritrea (2)
Haiti (1)
Honduras (0)
Laos (2)
Lithuania (1)
Malaysia (2)
Oman (2)
Saudi Arabia (2)
Sri Lanka (2)
Suriname (1)
Sweden (2)
Switzerland (1)
Zimbabwe (1)

Australia has a torturous internal nomination process, where potential T-list sites are generated by the State and Territory Governments. They last presented four sites to a now defunct Federal Government agency in 2009. What was supposed to be a fanfare descended into an embarrassing spotlight on the squabbles over one of the most promising sites - the Cape York peninsular. A further site - the West MacDonnell Ranges - wasn't considered good enough which left the remaining two sites (both extensions) going forward to UNESCO. Several potential sites currently have strong community support but haven't as yet got through the State Government hurdles.

I feel the Latin American countries stated above could certainly develop more extensive tentative lists. Honduras is already dealing with many challenges protecting their world heritage sites, while Belize seems not very motivated to nominate further sites.

I see 4 possible types of strategy with regard to forming a T List. At their extremes they can be described as follows - with of course a full range of intermediate situations between them
a. Shove everything possible on it - it doesn't cost much, there is no commitment required, it might attract a few tourists and publicity (there are examples in some countries of publicity which implies that being on the T List is something special!), it gives the impression that your government department is actually doing something and it might actually lead to improved preservation in some of the sites - either from domestic activity or from the attraction of external funds! There are political factors as well - internal ones such as a desire to "satisfy" different regional/ethnic interests by seeming to give their aspirations some credence and external ones such as the desire to at least be appearing to be taking part in the UNESCO activity
b. Only put sites on where there is genuine intention and capability in progressing them to a timetable and activity will take place to do so once a site is added to the T List.
c. Don't bother too much since nothing much is going to happen however many sites there are on your T List! Either because the potential sites which are not on it list are already reasonably well represented from other countries or by a site you already have inscribed or else are really going to struggle to gain inscription and you really have other things to worry about in governing your country or because your governmental "capabilities" are not strong enough to bring many/any sites to inscription! Some countries may also have internal opposition to spending too much effort on preservation via an international scheme either for religious or xenophobic reasons
d. Actively and positively conclude that your country is already pretty well represented in relation to its size/what it has to offer etc, has no really "world class" sites of an unrepresented type and, as a result, just accept that your role within the scheme is less to regard it as some sort of national beauty contest but more to support preservation world wide by supporting its overall objectives rather then by devising a long T List. Also use other schemes such as World Biosphere Reserves, RAMSAR, European Heritage etc to protect your valuable sites. I know of no country (yet!) which has publicly adopted this stance. UK tried to with a proposal to a consultative exercise a few years ago but the suggestion wasn't accepted!

Even if a country is aiming more towards strategy b. it needs to consider how big its T List really needs to be! Whilst a few countries have had a rate of 1 or 2 inscriptions a year even a rate of 1 inscription every 2 or 3 years is a "good" one for a country which is "active" in preparing inscriptions. Many countries struggle to prepare and present even 1 site to the standards currently required and need a lot of help to do so. Those without any sites get a "fair wind" with the assessment from the WHC (despite ICOMOS's nit picking!) but those which already have some sites are going to struggle unless they have a site of genuine "World class" of a type which isn't already well represented. So, for many countries, even 1 successful nomination over the next 10 years is possibly a reasonable aspiration. Why would they need a large T List?

I suspect that the countries listed above as having a max of 2 T List sites will contain each of types b, c and d!

An example for type d: Switzerland

According to the website of the Swiss "Bundesamt für Kultur BAK" a revision of the Swiss T-list is currently not planned (updated 01.02.2012):

http://www.bak.admin.ch/kulturerbe/04307/04317/index.html?lang=de

There is also a link to the report of an expert group from 2004 (pdf in German, French, and Italian). They evaluated 22 sites, only 5 were selected for the T-list. With the exception of the Le Corbusier nomination all of them were inscribed in the recent years.
The proposal of the Gotthard railway was deferred. The site has the potential for a WHS, but the proposal should be made more precise and the decision of the owner "Swiss Bundesbahn" was still missing.
Swiss thoroughness - so I think we can't expect a new nomination from Switzerland in the next years.
Last year I read an interview with a representative of the Swiss Ministry of Culture. He said that Switzerland is adequately represented on the list. In particular, the existing sites are against an extension of the list, because the value of the WH label could be diminished if the number of the Swiss sites will increase.