It's not necessarily a high average, but how does it look in context?
In 1993, Avery's first year as a Spurs starter, he didn't finish in the top ten in the NBA. However:
In 1995, he finished 7th in the league.
In 1996, he finished 3rd.
In 1997, he didn't finish in the top ten.
In 1998, he didn't finish in the top ten.
In 1999, he finished 9th.
In 2000, his final year as a Spurs starter, he didn't finish in the top ten.
Of course, Tony Parker has yet to finish in the top ten once. But there are other cir stances involved. As we agreed, Parker is a scoring PG, not a pass-first PG. Also, consider offensive systems: Under Bob Hill, Avery finished 7th and 3rd. Under Popovich, Avery finished 9th - once, in three-plus seasons under him.
I don't think Avery's numbers are low in context; do you want 10+ APG from the PG position? That would be nice, but Stockton, Kidd, and Nash don't grow on trees.