Right, it's a bit early to call it a pattern, but it just seems like it so far. Just with the way multitasking and other iOS4 stuff came so late and now with the iPad 2 announcement, we got nothing and we're all betting/hoping for iOS5. It seems silly that a new product just launched and we have to wait later to get the software improvements that are timed for a new iPhone.
I agree with you outside of notifications. Those will have more of an impact on the iPad than the iPhone which is why I want some differentiation that does impact something of that form factor size. I think notifications will heavily impact both platforms and not more towards the iPad though. Using Notified Pro is a god send right now and I had forgotten how annoying iPhone notifications were until I used my wife's iPhone the other day.
So you're right, it's too early to say it's a pattern, but for what looks like two years in a row, shortly after the iPad is released, rather than when the iPad is released, do we get major software changes to the device. The only difference this time around though, is it seems like that we're hoping that these software changes will be more differentiating on the iPad this time around compared to iOS4.
I accept that the first iPad was the foundation and they only had so much time to distinguish the iPad as a tablet form factor, but I can't help but feel disappointed they said nothing with the unveiling of the iPad 2. So I'm really hoping that iOS5 will bring those changes. I'm ready to buy one if they announce widgets, tabbed browsing, and other things that make the iPad a bit more unique in usage. I'm assuming that notifications are a given at this point but I hope that doesn't somehow become the focal point and Apple thinks they did enough because of that for this iteration.