Question: Ref. Receiver seperation

[PSU-RICK]

I've seen several references to our Wide Receiver's not being able to get separation as one of the reasons for our abysmal passing attack. But I notice that our opponents WR's seem to always get open due our defense playing a zone pass defense. So does that mean our opponents are always playing Man to Man pass coverage? You would think that if our opponent plays Zone coverage then our WR's should be able to find an open spot once in a while??