Android can do this as well if you have the Backflip. This is not an OS limitation but a carrier one.
Why do you need "Backflip" ? I can send text messages, check my calendar, look at pictures, etc, etc while on a call.
And as you say, the ability to surf the web (actually, anything that uses data), is a CDMA shortcoming, not the fault of the phone or it's OS.
I was referring to the Droid X that was being discussed. Sorry if I wasn't clear. Most of the Android phones seem to be on Verizon, which doesn't support simultaneous voice/data.