I see the opinion that teams should keep drafting QBs until they are "sure" they have the guy, a lot. So I wondered, how many of the current starters in the league were acquired that way. How many were drafted by a team with a developing or established starter (as opposed to a team whose QB situation is a mess or a QB at the end of their career) and were picked as an insurance policy of sorts.
I can find one definite - Tom Brady (he almost doesn't count because even NE didn't know what they had drafted).
A couple could be looked at that way - Schaub (although he was originally drafted by Atlanta and was never really considered a choice to start for them), Foles (interestingly Vick was also the starter when he was drafted and Vick is very late in his career).
Drafting an "insurance policy" at QB in the 2nd, 3rd, or 4th round just doesn't happen. Teams stick with their QB until they decide he is not the answer.