I won't dispute whether notifications was ripped from Android, but calling Notifications the "most fundamental" feature of iOS is an incredibly huge stretch.
If you ask 10 iPhone users what the most fundamental feature of iOS was, you'd probably get 6 or 7 different answers.
It was the first phone browser done right, and is still arguably the best. Outside of the phone operations, I would trade away every possible feature of iOS for Safari.
Notifications is an annoying piece of crap for a lot of people including me. That isn't to say the previous generation of alerts were not worse, they were.
But I highly doubt that many people think it is THE cornerstone feature. For some, like me, it's Safari. For others, it's FaceTime, others the camera, etc.
I think Safari still doesn't auto-highlight the text in the search box (my most used browser function besides actually scrolling a page), so annoying to start typing a new search time and realize it's just adding on to the last search time until I hit the x. I guess Safari now at least syncs tabs and bookmarks with the desktop version, but still it's a stretch to say it even competes as a top mobile browser IMO.
I think notifications are only annoying on older iOS versions. In Android they've always been unobtrusive, and with Android 3.0+ (and especially in 4.1) they've got a lot of added useful functionality.
But to get back to the point I would say the defining feature on iOS is proper group texting. So, yeah, that's a lot of quibbling words to basically agree with your point.