Different payment models coupled with Microsoft semi-abusing their monopolistic state.
Microsoft have no reason to implement such a system, you've already bought their product and they won't see any money from you until you buy your next computer (most likely) so, they've no motivation to keep you loyal. following on from that, because MS have such a huge install base it's unlikely your next computer will be running another OS.
On the other hand Blizzard have people paying monthly. If they don't like the service they're much more likely to leave, so it's in Blizzard's interests to keep them as happy as possible and stop them going to another MMO.
I also don't think the error reports ever get looked at by anyone at Microsoft. One of the first things I switch off anyway, I just want a "close" button. Plus many of mine are from debugging my own software, which I'm sure MS aren't interested in.
