Since Bethesda has announced that Dawnguard might not even make it to the PS3, I thought I would share a tidbit of information about Bethesda.
Bethesda is not stupid, they know how to program for the PS3. The performance issues on the PS3 are intentional, as they are making A LOT of money from Microsoft to make the game basically exclusive to 360 (the PC release isn't under scrutiny because it's still Microsoft and most people who choose PC Bethesda games over Console ones aren't the same demo as Console gamers due to the prevalent modding).
It's disgusting what Bethesda is doing and even more disgusting that Microsoft is using these tactics to muscle-out Sony from the market.
I'm not saying Bethesda is this all-great Developer, but a vast majority of the bugs in the game are present in the launch because Bethesda doesn't do much Beta Testing. In fact, Skyrim had NO BETA TESTING whatsoever.
A lot of games have game-breaking bugs after the initial round of coding, but with proper testing and improvements the game becomes less buggy. The reason Bethesda chose not to Beta Test was because they really wanted that 11/11/11 release date, though they still could have tested the game if they were a competent developer.
This has been going on with Bethesda for awhile, with just about all of their games. The team that works on PS3 ports is considerably smaller than the 360/PC teams and they're not given as much time to work on their PS3 ports as their budget is smaller because they are given huge incentives by Microsoft to make their games unofficially exclusive.
Again, I'm not saying they're a perfect developer, but they're not stupid. How could anybody really believe that a Developer/Publisher as big as Bethesda can't program properly for the PS3? That's being way too naive.
With that said, It's very possible that Dawnguard will eventually come to PS3, but how long it'll take and how well it'll perform is unknown.