Do they get the choice to?
It's not like I can get a less buggy version of MS Windows by paying an extra $20.
And while many open source projects accept donations, and many enterprise products offer support contracts, it's not like $20 gets you a guaranteed bug fix.
I agree with your point that companies don't always have a good business case to produce quality software - but we can hardly blame customers for not buying things we aren't selling :)