I agree, there is several reasons why everyone isn't using the iPhone, or Blackberries, or Android devices, etc..

As far as I'm concerned the more variation we have in hardware the better (as long as applications are decently compatible.. of course an app designed for the N900's specs may not run well on a device that doesn't have a similar CPU speed). Want a really nice camera and you don't care as much about applications outside (Twitter, Facebook, and some GPs app?). Get the N8. While someone else may want lots and lots of storage. Or someone else might want a hardware keyboard. And so on.

As long as you can run the same app across the various devices (constraints due to spec capabilities and hardware [e.g. if your don't have multi-touch obviously multi-touch won't work) then who cares.

That's what I think Android is the platform that will outnumber everyone in the future, simply because of variation in hardware but some compatibility across applications. Though I did hear an interesting argument that the iPhone will likely remain the platform for mobile games (excluding Nintendo and Sony due to game differences) due to somewhat standardized hardware (Windows 7 Phone Series too due to Microsoft's standards and XBOX Live compatibility). And if Nokia can pull off what Android is doing (wide variation in hardware, but with application compatibility) then I think Android will have itself a competitor.

If Nokia and Intel can't do it, then I think the future will be Android with the main marketshare, Apple, (maybe RIM), Microsoft, (maybe Nokia), with smaller marketshare.