There seems to be a randomness about this whole thing. I don't show an update on my iPhone 4S or iPad 2, but a coworker (same carrier and wifi network) has it available on his iPhone 4 (and he doesn't even want it yet since many features don't work).
Is there an interval between checking? My iPad doesn't even seem to check when I select software update. Just tells me it's up to date (with a seeming disdain for my plight).