Flameouts (32 or fewer starts): 9
This includes guys like Johnny Manziel, Jake Locker, Matt Leinart, JaMarcus Russell, Brady Quinn, Tim Tebow etc.  Guys who lost their starting job early or never managed to win it

Didn't make it to end of rookie deal (64 or fewer starts): 10
This includes guys like Josh Freeman, Vince Young, Marcus Mariota, Byron Leftwich, Blaine Gabbert, Kyle Boller.  Guys who were good enough to get through the (most of) the rookie deal as a cheap starter but didn't show enough to get that next big contract as the starter

Made it to the next deal, but not a franchise guy (128 or fewer starts): 10
Here you have the guys who were good enough to get an extension or keep the team on the hook a bit longer, but ultimately weren't the answer (Jason Campbell, David Carr, Chad Pennington, Mark Sanchez, Blake Bortles, Sam Bradford).  Of the 10 on this list, only 3 are over Sam Bradford's 83 games and they're all special cases. 
Andrew Luck (86 games) was a franchise QB who called it quits early
Mike Vick (115) was also franchise guy, but missed substantial time for other well-known reasons. 
Ryan Tannehill (121) will have graduated from this group by the end of the year.

Franchise guys (128+ starts): 11
This is what you hope for. The worst case in this group is Cam Newton, Jay Cutler, or Alex Smith.  But it also includes guys like Aaron Rodgers, Matt Ryan, and the Eli/Ben/Philip triumvirate.

Long story short, if you get over 85 starts, you're almost certain to get 150 or more.  There's basically 3 groupings of QBs

1. Busts

2. Those who are "just a guy".  They get 60 +/- 20 games. 

3. Franchise guys.  They get 200 +/- 50. 

That's why an O/U of 124 (Jeff George) for ZW is so interesting, because it puts him in between those two groups, which just doesn't happen (barring repeated injuries, jail time or a late explosion onto the scene, which isn't a factor for 1st rounders)