Hint: When Siri came out, everyone with a Droid phone wanted it too. When the feature complete competitor comes out in full force, probably in Android 5? they will all be hilariously frustrated with how they can't use it because they have a 2 year old phone.
In fact I'm not sure I understand why Siri isn't available on the iPhone 4/iPad 2, etc.
Google is endlessly iterating their core service applications - mapping, navigation, voice recognition, gmail, places, and so on. With Chrome they are quite welcomely decoupling the browser (long overdue), though that is one of the only major dependencies on ICS.
The notion that the operating system needs to iterate for Google to move the base forward is not accurate.
Which is interesting seeing the focus on ICS, which makes me wonder whether we're past the point of diminishing returns. People desperately wanted each of the prior iterations because they fixed fundamental flaws in the operating system (e.g. slow runtimes, bloat, etc). From Gingerbread to ICS, however, is largely a "meh" affair on smartphones. Of course new devices come with it, but for the existing base it just isn't that compelling.
Honestly I see virtually no difference between 2.3 and 4.0 on the Galaxy S II when it comes to scrolling, etc. Indeed, if you turn on the development option that blinks the screen red when the main thread is blocked, it occurs all the time in the basic operating services and in most apps.
Which correlates with the argument made by Hackman (? Hackwell?) regarding GPU offloading not being the actual issue: Instead it's the OS still not, essentially, giving enough respect to the UI. This still isn't a solved problem, beyond simple brute-forcing it (e.g. a HTC One X).