How many Sámi are there?

Lars-Niila Lasko has written in his blog about how many Sámi there are (http://lasko.bloggsite.se/post/769/7078). The official figure for Sweden is 17500. This figure was, as he writes, produced many years ago by taking all reindeer herders (a minority among even the Sámi!) go back two generations and calculate their relatives today. This was done in the seventies. The figure is ridiculous. Lets calculate how many Dutch there are by taking all cheese makers and their relatives... Or Swedes: all who work in forestry and their relatives.
(important to know that ethnicity is not registered in Sweden which makes all figures just calculations)
Another research institution calculated some years ago 65000 Sámi in Sweden, and this is more plausible, even if that also may be a rather conservative figure. They also took existing litsts of reindeer keepers, voting lists for the Sámi Parliament etc and calculated their relatives.
One wonders why then, the 17500 number is still used officially as the number of Sámi. Do the authorities not want to have too many Sámi? I don't like to believe it is that bad. But why?
Maybe the best guess today for swedish Sámi would be something between 60 000 and 100 000