Using it as a factor, though, leaves you with cases like Archie Manning, where the team was so bad despite him that he had a career 35-101-3 record. Put in the right situation, it's probable that Manning would be in the Pro Football Hall of Fame. For that matter, I believe Tony Romo should be put into the Hall of Fame, but I don't believe that he will be because of his team's lack of playoff success.
We do not judge running backs like Barry Sanders on the basis of how many games Detroit won, even though obviously he was a big factor in any success the Lions had during his time there. We don't do it with any other player but quarterback, when they also only play a role in any success or failure.
I think won-loss records are given too much emphasis with QBs, and that's a shame, because some really great ones just ended up in some really bad situations. The only way I believe you can use it as a factor is by judging the whole team and whether the contributions of that QB made the team better than it was, even if it has a poor record. That takes far more effort than just looking at numbers, and most people are not going to go that in-depth. Other statistical measures also have flaws, but won-loss records are just a bad way of viewing QBs.