Please share this with your developers:
The Dawnguard/PS3 problem may have a fix.
If the problem is due to huge save files and ram issues, it's possible to alleviate these issues by removing useless items from the game.
On Fallout 3, a PC mod came out which removed a certain rock from the game. By removing this useless item, which repeatedly reappears, it reduced save files and led to much better performance.
This could be done with Skyrim. Imagine if the linen wraps, soul gem fragments, and countless other useless items were stripped from the PS3 version of the game. It would free up tremendous system resources, and reduce save file bloat. Then Dawnguard, and future expansions, would have a much better chance of running smoothly on the PS3.
Please pass this on to your developers. They may have considered this idea already, but if not, it is worth looking into. I can asssure you that PS3 users would not miss these items, and would be thrilled to have the DLC available to us.
Thank you.