I was wondering the same thing - my guess is that they added this hastily (maybe that's the wrong word; I"m sure it's not trivial to change) and haven't figured out how to remove all the sizes from the system.

If anyone else knows, that'd be helpful - I'm thinking of just buying a ton of *.smalls...

// Edit: Oops, maybe I misunderstood the parent. Sibling's right; you'd need 256 small RIs to make up for one 32xlarge RI. I'm wondering why we should ever buy 32xlarge RIs and lose granularity.