LJ,
You can do the same with the C295. The biggest issue with the Q400 and the Sea Herc is that they only exist on paper. I very much doubt that MoD would wish to gamble on being a lead customer with all the cost of R&D, T&E etc, plus the experience from both the AEW3 and MRA4. COTS removes the uncertainty of the gamble.
However, we shall see what Father Christmas brings in SDSR 15 eh?