Chad actually says that Olshey was the one to suggest that comparison, and he seems to agree with it only in regards to their temperament, pick-and-roll abilities, and overall athleticism. Personally, I think Billups is a pretty favorable ceiling to project for an untested rookie, and there's no way I'd start throwing around names like Rose until we've seen a bit more.
In shootarounds I saw Leonard frequently take shots just inside the three point line, and he made a surprising number of them. I never, ever remember Joel doing that. He didn't take those shots during SL games, but I can see him developing into a Raef LaFrentz kind of center maybe. He's remembered now for taking 3's and the RLEC debacle, but truth is he was an excellent shot blocker before injuries ruined him. Oh, and he's a white center. lol.
Leonard seems to have better hands than Joel - so I suspect he will be much more of an offensive threat, with time, than Joel ever was. Not that there is anything wrong with being a nasty mofo like Joel.