I'm sure they are making a lot of money by selling statistics from all around the world to big companies reselling that info again. WikiPedia KNOWS WHAT WE ARE LOOKING FOR and much more
Everytime they're in need of some extra money the "Donate to WikiPedia" frame is on their website too. So they easily get $6,000,000.00 in one month by doing that. They probably have private investors too.
Well it's one big deal about money, Twitter is the same -- they have no ads, but are making money by selling information to companies that use them to make up statistics etc.
Yes, Wikipedia has tremendous support and deserves it. I always donate $10