I've heard the same predictions about linux in general for 15 years.

Even if Android is #1 commercially, it won't stop from a large variety of mobile Linux disto's from thriving. And android with its Linux kernel will actually help this because drivers will be available for hardware.

Looking at n900 there ae still some close components, some drivers and some phone and messaging apps. But the apps could easily be replaced (think FSO.)

More over I am fairly sure at some point android will emulated on linux under X or what not, allowing for use of android apps under other distors. Its simply a matter of time.