Or, put it another way, QBs in the top 10 since 2004 who sat their whole first year:
Phillip Rivers
Jake Locker
Matt Leinart
JaMarcus Russell (moreso his own fault, but I'll put him here)
QBs who started in their first season:
Eli Manning
Ben Roethlisberger
Alex Smith
Vince Young
Matt Ryan
Matthew Stafford
Mark Sanchez
Sam Bradford
Cam Newton
Blaine Gabbert
As you can see, more often than not, a top-10-drafted QB starts a game in his rookie season. Those who sit have either been busts or the jury is still out (Rivers and Carson Palmer before him are the exceptions, but I'm picking 2004 as the line of demarcation because the rules that benefit the QB were put in place after the Patriots clutched and grabbed their way to a second Super Bowl). The jury may still be out on some of QBs who have started a game in their rookie seasons, but there's no doubting that A. most of them did have at least 1 start and B. you're more likely to hit on a QB that you can get to start in his rookie season than if you sit him, ESPECIALLY with the rules protecting the QB and receivers these days.