Ummm, I'm not sure that's true. I definitely had his stuff drop on the last couple of play throughs regardless of whether I summoned Leroy. Maybe it's a patch thing.
@quadfather - Exactly that! It's like the Beatrice drop in the Valley of the Drakes, unless you summon him and conesquently keep him alive for Pinwheel then his stuff won't appear at all (apart from the humanity and the souls that he drops). Also bear in mind that there's a gamer called Paladin Leeroy who only ever invades in the same area on PSN - which confuses some people into thinking that the real Paladin has showed up.