As a non-triathlete, I have to agree that it's about quality much more than quantity.
Every one of my 4100 bici miles this year has been
"junk miles." Most of the time I can't even be bothered with a sign sprint. I just like to ride and I don't pretend it's doing me a whole lot of good.
Running is a whole 'nother story. I'm not fast, but I've been able to get faster and run farther by trying to make every run count. So I was able to finish my 1/2 two weeks ago with a time I was quite happy with, on an average of less than 15 miles per week.