Actually, both Pac-Man and E.T. were developed and published by Atari itself. That's not to say that third-party garbage wasn't a major (and probably the primary) problem.
I actually owned and played both those games on the 2600 when I was a kid. As it turns out, they were very buggy (and for me to recognize this as a child says something). Not refuting your point, just an anecdotal comment.