While I don't rule out that the PS3 port of Skyrim is a crap translation done as an afterthought, there are some technical constraints to the PS3 hardware that would make it very difficult to get a large open-world game such as Skyrim to work, and be able to extend it with DLC. The most important one being the memory model, where you can only access 256 of the 512 MB RAM directly from the CPU.

Most other games 'solve' the memory limitations of the PS3 by chopping up the game world and introducing lots of load screens, or by streaming as much of the content as possible. My guess would be that the Skyrim engine does the latter, which doesn't fit the PS3 memory model very well. The Blu-Ray drive is very slow for random-access, and I don't think you can stream textures and geometry directly to the 256 MB RAM segment accessible to the GPU, which means you would have to allocate part of the already-scarce 256 MB RAM in the other segment, and DMA it to the GPU-segment.

I'm not a PS3 developer and I don't know anything about the Skyrim engine, but it's well-known that the PS3 memory model can be a real PITA, and I can imagine this makes it very hard to get certain optimizations that work well on other systems to work on the PS3.