If you type "900 mhz" into a google search, you can also get an idea of the sutff that doesnt play well together in that freq range. Like cordless phones, baby monitors, etc.
I think 900 mhz could have been better than 2.4 from a signal penitration standpoint thou. And 5.8 ghz I think is much worse than 2.4 in that regard.
Think about the issues weve seen with 2.4 signals not getting through some aircraft fuses and how much more critical antenna placement is vs. the 72mhz stuff. Seems to me that 5.8 would require all antennas to be outside the fuse to get a clear signal. Just my guess thou.

Fun stuff.
Cheers.