I'm not entirely sure on this, but if the 5400 RPM was partially due to a shift from a 3.5" to a 2.5", wouldn't the speed drop be not as bad?
Awesome write up by the way, thanks for adding a bit of sensibility to these forums. Turns out putting the best mobile GPU into an iMac isn't enough for some people... perhaps they envision an all-in-one that's as thick and heavy as a Mac Pro.
Only real decrease, other than the 5400 (personally I've realised that if you care about that stuff, you'd be better suited to a 27" - I'm selling my 21.5" and would only replace it with a 27"), is the loss of the optical drive. I'm very surprised that people care that much. I suppose people will never be satisfied.