Many bugs only get discovered after game release though... There's a big difference in testing before release, which is done by a limited amount of people, and thousands of people playing it after release.
Not an excuse but a plausible explanation.
No number of refunded games will alter that, on the contrary, it might cut the budget of support...
Not saying having the game refunded is a bad thing, that's something everyone has to decide on his own... But the reasons above won't change anything IMHO