You do rely on one supposition: You rely on the assumption that the people who buy the Android phones will be 100% satisfied with their phones when they decide to buy a tab. The problem with that assumption is that I personally know a few Android phone buyers who already don't like it, even though they've only had their phone a few months. They can't back out of the contract due to going past that 30-day grace period, so they have to keep what they have until their contract expires. One of these people in particular has already told me she's going back to Blackberry as soon as she can--which means she'll probably buy a PlayBook when she chooses a tablet.
The point is that of those tens of millions of people (there's only about 80 million iPhones out at the moment, so give Android similar numbers, though in all honesty the installed base is probably half that right now) some percentage will not like Android any better than they like iOS, or decide they like iOS better. These people will look for an alternative, which is currently either RIM, Nokia or iOS. End result, we honestly don't know where the market will be in another year, when the first round of Android contracts expire.
Oh yes, of course, I appreciate I was making it simplistic to make a point.
Android will get better on Phones, Android will get better on Tablets, Over the next 5 years I expect Android would/should be way advanced than it is not on both types of device.
If people are happy with their Android Phones then they may also be happy to consider a tablet, perhaps which also runs the apps they like.
I would expect Apple people with iPhones also would be more lightly to go with an iPad than an Android version.
Not all, and of course there will be some crossing over.
End of the day I can see two things happen.
Apple goes all out on hardware and the OS and rides high at the top of the pack and shows everyone how it should be done.
This would be great.
Or Apple give up, realise they can't fight against the mass might of the other tablets, and like the iMac, sits in the background, thinking it's right, showing off a fancy design, whilst not bothering to keep up to date, relying on a loyal fanbase.
At the moment, they are way out in the lead, so they have now the chance to make themselves the leader this time and stay there.
My only concern actually is Steve Jobs being pig headed and holding the device back, not now, but in a few years time.
I hope he does not do this again, and pushes and pushes.