Why? Do you think that Apple would be not be better served by a special team whose chief mission is to orchestrate new iPhone OS-based platforms?
Do you think it's better that Apple divert engineering resources from their normal teams and jobs every time there's new platform development? Do you think iPhone engineers should be ripped away from the next generation iPhone in order to get device drivers running on the iPad?
I read numerous times that this is exactly what has happened. I think Steve even mentioned this in his keynotes a few times (but not in that wording of course). OSX seems pretty stagnant since 2007, save for a couple of features (which I have not benefited in any way from from). Their current pro products use outdated technology.
I use my computer for both serious work and for surfing the web. I love Apple products, but I have no loyalty to any company. If they neglect their pro products and applications, then I will have to look elsewhere.
I can see them leaving the traditional "computer" market all together. They will go where the profits are.