But here is the thing: That would be a LOT more effort to make what will inevitablye result in a group who bitch about being "second class citizens" ("Oh mah gawdz!!! I have no achievements or cloud syncing?!?!? YOU GUYS SCAMMED ME!!!").
Patches will involve making multiple versions (and probably a return to the madness that was incremental patching). They'll need places to store those patches and that will greatly increase the difficulty of tech support ("THis don't work... wait, there was a patch five years ago?").
And sadly, I don't think it would help. Don't get me wrong, a LOT of people would like that. But it isn't a deal-breaker for them. The people who say "I refuse to pay for this because it uses Steam" will, by and large, become "I refuse to pay for this because it uses incremental patching". There are, sadly, always going to be people who just look for an excuse to bitch. No citation for that, but I think it falls under common sense (so ignore it if it doesn't support your argument :p).
So it would be a case that might make a bunch of people slightly happier at the cost of greatly increased support costs and an arguably negligible (long-term) impact on sales.