Hmm I'm not putting blame on the wrong place? It's Todd Howards fault because he wants money haha
Yes you are.
Xbox 360 and PS3 both have 512mb of RAM.
Xbox 360 uses its RAM in a type of "pool" so it isn't dedicated to just one system or the other.
PS3 divides its RAM, so only 256mb of it goes to the GPU.
Skyrim needs more than 256mb of RAM in the GPU and CPU, it works with the Xbox because it doesn't use all 256 at once, most of the time it goes over. The extreme lag from the beginning of the PS3's time with Skyrim was affected by this division of RAM (which works well for games that are specifically coded to the PS3, but not for multiplatform). Most likely, the system can't handle running the game and multiple add ons at once, so they have to heavily recode Dawnguard and all future DLCs for Skyrim on the PS3, another reason why Sony is working right with Bethesda on this.
It has a possibility of not even being on the PS3 because of if Dawnguard has to be recoded to some extreme lengths, then it may not even be compatible with Skyrim.
Sony wanted to be "unique," so they made their own architecture in order to get the most out of what they had. They did not stop to think that it could hurt multiplatform developers, and then by that, the consumers.
The PS4 won't be like that, so don't worry as future multiplatform games should run just fine on the 8th gen consoles (except the Wii U).