You should be grateful for the delay.
Even though us PC owners have received Dawnguard a month after X360 owners, it sure was buggy as hell. At first I couldn't even start the game with it installed. Took an unofficial fix for me to play the blasted DLC without forcing myself to switch the base game's language to English. Quite a nasty surprise. Not to mention that most gameplay bugs from X360 are carried over to the PC version of the addon.
And the main reason Bethesda delayed the PS3 release is to make it a more steady, less buggy experience.
And despite that, they receive rants from people like yourself.
I stopped wondering why they release such buggy games in the first place. They just feel rushed by fans breathing down their necks, saying "release the damn game already!". I'd be almost expecting to see a big studio NOT count with players and just release a buggy product, telling players to go to hell if they don't like it. But no, they keep working to polish the game despite it having been released almost a year ago. Try comparing that to 2K Marin for example with their BioShock 2. They stopped issuing patches for it despite half the bugs remaining in the game and they were insolent enough to claim some bugs were fixed when they obviously weren't. To top it off, the last two patches were there only to make the DLCs work with the game. DLCs that have been initially cancelled and then horribly delayed before finally being released. And even now they're working only for half the playerbase judging from what I'm reading on their forums.
Face it. Sony is a bitch. It's expensive to publish games on their console, it's expensive to release downloadable content and patches for their console. You get less shots than with Microsoft, so you have to do it right. PC, X360 -- we're all gonna receive patches for both Skyrim and Dawnguard eventually. PS3's.... they might not be so lucky to receive as many patches so any product released there, including DLC, must be done right in the first place.
And the truth is, in its current state, Dawnguard feels a bit like an unpolished beta. Just wait patiently. It's way better than pushing Bethesda to release it just now.