The webpage on Panthera tigris of the IUCN Red List http://goo.gl/hV5nj explains that that value of 3200 —which was the IUCN Red List baseline estimate of that time— was agreed by the Tiger Range Countries in 2009. These countries have already updated their estimates (International Tiger Forum, St Petersburg, 2010) to a value of about 4000 adult animals globally. Further, this webpage warns about estimates of tiger status outside protected source sites, noting there is evidence of a breeding total of only 2154 tigers in such sites.
It is worth noting that the value of about 250 tigers for Thailand is the upper limit of the 2010 estimate of Thailand's Ministry of Natural Resources and Environment http://goo.gl/yNOpz whereas its lower limit is of c. 190. Most tigers there are in the Western Forest Complex, especially in the sanctuary the blogger visited. That she did not see a single tiger during her daytime visit is hardly surprising: a solitary species (which usually eschews human-activity areas and is a predominantly nocturnal hunter), the estimated density of tigers is that sanctuary is about 2 animals/100 sq kilometers.