Pittsburgh, Dallas, Miami, and Atlanta all averaged between 23.0 and 22.5 ppg last season. Do I expect Matt Leinart in year 5 to perform as well as Matt Ryan in year 2? Yes. Yes I do.
22 ppg is the league average. I expect Matt Leinart to lead an above-average offense, because the offense has above-average personnel.
I know that we're all involved in Kurt Warner hagiography right now, but Warner wasn't as good last year as he was the year before. In 2008, the offense averaged 26.7 ppg. That was out of hand. Whether people want to admit it or not, Warner did a lot more game management this season.