Bethesda ruined Oblivion on their own. Xbox was still brand new and not holding anything back with its old hardware, as it wasn't bad at the time.
Xbox ruined Dragon Age II.
Xbox ruined Crysis 2.
Xbox ruined RDR and L.A. Noire.
Xbox ruined Fallout 3, but it was decent anyway.
Xbox ruined Fallout: New Vegas, but it was an exceptional RPG in spite of this because of Obsidian's writing and worldcrafting.
Xbox ruined Skyrim too, but Skyrim will survive well enough to be a good game in spite of this. For all the simplification and dated visuals I think Beth's learned enough from their failure with Oblivion and partial success with Fallout 3 to make a good RPG again.
Remember: Morrowind had terrible gameplay for the most part. It was the freedom and richness of the world, atmosphere, and the writing that made it exceptional. I think Beth understands this again. So yes, Skyrim will be a vastly lower quality game than if the Xbox and PS3 didn't exist, but it should still be good.