For many corporations, the legalese related to things you create while under the employ of said corporation is rather extensive. Truth be told, there is a lot of boilerplate in there and most corporations are really only interested in stuff that competes with them, so it's more for defensive purposes than anything else.

That said, the language used is rather deep and entirely one-sided to the benefit of the employer. I would be surprised if any major corporation didn't have a clause of that nature in their standard agreements.