Not sure why everyone wants to tie TD passes to INT's. They aren't really related.
For many years, I've seen TD/Int ratio as one of several generally accepted performance metrics for quarterbacks. I guess over the years it's become somewhat of a benchmark. I don't have any numbers in front of me at the moment but I would guess that most successful QBs throughout modern history have ratios higher than 1.0 in years that their team was successful. But like many have pointed out, the ratio is not totally dependent on the QB's performance even though he usually wears the good or bad label that goes along with it.