Yes, but some people (and I can't say I agree with them, but hey...) like to play grunt, as in Big, Stupid dude that Hits Very Hard. A character like that couldn't cast Open 100-100 because he has an Alteration skill level of maybe 5, which would give him, what, a -273% chance of casting the spell?
The advantage of shelling out the mulah is that ANYBODY, from a Telvanni master of magic to the most gruntish Redoran warrior can use the ring/belt/whatever of Open Everything.