Actually you have to take the process one step further. In the early seasons (at a minimum) teams had to sign or otherwise fill out visa applications for some of the countries (the producers were able to do this for other countries) and this would be done before the final selection of teams during the final interviews.
The teams would see visas for countries in their passports some of which were not going to be visited. Another thing to keep in mind is that the producers would have to have visas for backup or alternate legs as well as the primary destinations that TPTB plan to go to for that season.
So the presence of additional visas isn't just to obscure the actual countries the teams may visit, it's also to have the paperwork done for countries that may have to be used at the last minute.
Might be a good question to ask some of the recent season racers, especially since the question keeps coming up.