I'm sure the PS3 version will be just as good as the 360 version because Rockstar like Infinity Ward focuses on quality.
As for the advertising there are a lot of possibilities... 360 GTA IV, Halo 3 Bundle? I am sure that if it is a Microsoft commercial it will sound like it will be exclusive to Microsoft. Don't expect any Sony logos. And the commercials were probably part of the $50 million agreement. I would also expect some preview of the DLC to further sway potential buyers.
As for sales... I think GTA IV will meet Halo 3 in sales (The install base will be about 5.5 million more then when Halo 3 was released). If you look at the numbers, Microsoft paid $50 million for DLC. Assuming DLC is about $20 a shot, they are looking for DLC sales of about 2,500,000 to break even...