That's just it. When considering a QB for the HOF, you have to view his performance/success relative to the peers of his era.
Rivers' cumulative stat rankings are impressive, but he's been doing it in an era when every QB worth a damn is throwing for 25+tds and 4000+yards every season
For most of Marino's career, 15tds and 3000yds was considered good production for an NFL QB, which illustrated how dominant Marino was, when one considers his average season.
Rivers' will get HOF consideration when the times comes, but I just do not see him getting in unless he leads the league in TDs pass a couple more times and/or wins a championship.
He also has the obstacle revolving around the question of just how many QBs from this era are they actually going to vote in?
Peyton, Brady, Rodgers and Brees are locks, which is probably going to make it harder for guys like Ben and Eli to get in, let alone Rivers.