Actually it is quite important that the N9 be OMAP 4 for customers. First, The OMAP4 has about the same power usage as the OMAP3, and the idle power usage on the OMAP4 is lower than OMAP3 (at least from the older 65nm OMAP3's). Another thing, the OMAP4 has better memory bandwidth, and AFAIK can support more RAM. Last but not least, the OMAP4 supports 1080 output and a higher resolution camera then the OMAP3.

So having the OMAP4 will have quite a few benefits that the users will feel pretty well, so there is a reason everybody is moving to these newer processors. Also, I don't see how this has to do with Apple, but never mind.

Last but not least, Maemo/Meego needs more horsepower then android or iOS. You see, android has changed it's stock linux in such a way so that most programs written for android will suspend and stop running, in addition android doesn't use swap. The kernel in android was modified to wakeup less often, and the graphics layer was rewritten to be more lightweight.
Meego on the other hand is closer to stock linux and as such can use swap, and it's apps are multitasking by default without needing some flags. (Meego and WebOS are the only truly multitasking mobile OSes). In the end it is heavier (but can provide more features) and will benefit much more from a more powerful processor.