I don't disagree with your premise, but the killer feature for me on a device with the full "gapps" suite is Google Navigation (the full Maps + turn by turn), not the Market, and it would be far more difficult for anyone to replicate Google Nav than it would be to replicate the Market, IMO.

Of course, Nav is more relevant to phones than tablets, but I wouldn't even consider any Android phone that didn't have Google Nav.