It's just a guess, not a certainty. Your mind seems pretty made up about Mint without knowing all the details surrounding the acquisition.
What's kind of funny is the vast majority of the 37signals philosophy I agree with. Hell, we turned down VC funding in part because we really liked what you guys were able to do without it, and the fact that investor interests and founder interests often conflict. But to lambast someone for taking the payday of a lifetime without knowing all the circumstances surrounding not only their company, but their life, doesn't seem right.
I think the post will end up being contrarian just to be contrarian. This site and YCombinator were created as a result of "fuck you" money.