I think that's the main reason Zenimax wanted them. They can use id as their internal engines team and get incredible tech for their other companies. Personally, I love that idea, being an old-school Bethsoft fan; they've always had incredible designers, but their engine tech has always been either a poor in-house engine, or a hacked apart version of an existing engine (e.g. NI, now Gamebryo).
I can't wait to see TES5, running on an id engine.