Ah, yeah, it's probably not true for d20. Likely one of th'varying differences between Inc and it.
And maybe a cap, I'unno. S'like I said, that sort of thing happens pretty much only with gremlins* and it's more than a little thematic for 'em. Plus of the stuff it happens with, only the gremlins are particularly mobile. Not exactly a high priority issue, aye. Leaving it be wouldn't be a big deal, in m'opinion, and it's a fairly neat thing. E: Though maybe cap xp gains (on a per dungeon level basis, if possible) and squelch corpse generation for multiplying creatures. Orcs in particular get giddy when they run into a multiplying critter, since each corpse consumed will probably give a little XP. Several dozen corpses...
*Well... and a few others. Brown molds, sometimes blue jellies and brown puddings, but of those only the molds can happen autonomously. Brown mold infestation of a lava stream is something best just left alone, though not because of the amount of 'em. They get more max and min HP the more fire damage they take, heh. Three, four thousand HP mold? I've seen that. Dozen member multi-thousand HP mold swarm? Yeeeeuup. Just... walk away. They're slow.