I'm an ex commercial pilot, now software engineer with 15+ years of experience writing real time avionics software. I'll definitely be getting an iPad to go along with my Macbook Pro and iPhone. You'll find many engineers with macs not for the looks but for OS X and its UNIX/BSD base combined with its excellent integration with the hardware. Most of us used windows once upon a time
The reason full OS X is not being supplied is due to it's performance on the power efficient processors, have a look at the reviews of how windows 7 is performing on tablets ... not well at all.
Why are so many developers supporting the iPhone/iPad? The App store takes away all the pain of having to set up a commercial site and get customers in. + the huge user base. Apple also produces one of the best development environments money
can't buy, it's been free for eons.
Unfortunately due to certification requirements, it's too difficult to get the iPad/iPhone certified as a navigation device due to OS X and the hardware operating limits. The OS would probably have to be qualified to Do-178B Level B or C and Apple would not be interested due to the cost and limited market. However it would make for a great planning and briefing device.