Because only people part of the beta programs with Apple are legally allowed to have the 2.0 software right now. Directly linking to the beta software on most forums draws the attention of Apple's legal department, so I'd imagine trying to sell an iPhone with the 2.0 beta software installed would draw their attention as well.
Then again, most people don't realize that they can get 2.0 if they really wanted to for free...but even if he was a legit developer, wouldn't that be a breach of Terms of Use?