While I agree that pre-snap some QBs will notice a 1-on-1 matchup and will throw to a certain WR b/c he recognizes a mismatch. I rarely think when a QB drop backs and has to go through his progressions/options he says, "oh Webb is playing him let me throw his way". A QB usually has less than 4 seconds to make a pass, that happens so fast, the QB is looking for the receiver that is open regardless of who's defending him. I read a comment from Flacco yesterday, he basically said he's gonna throw to whoever is open even if that WR/TE is being defended by Reavis.