In game advertisments...
could help sony get a little more money back from the current user base, but it will certainly scare away most new users, who rather pay for their network access (xbox360) than get ads while they are playing.
On the other hand, the wii has open internet access (with the opera browser) and you can actually own the titles you purchase and play web based games with pc users. Sadly the weakest platform (the wii) seems to be the only one that is at least partially open for users and hobbyst developers.