I had typed a long post and hit Submit when I got a message that the board was being updated. Who updates software during the middle of the day? Mods, if that was your call, I am disappointed in you.
Any way, to answer the question (and it is a good question), you have to remember that DBs must constantly react to the play. In running a route, the WR for the most part knows where he is going ahead of time, and the DB must constantly react to his movement and the ball.
This puts a DB at an inherent disadvantage against the WR. There are tricks a DB can utilize to lessen that advantage (Aaron Glenn was a master at this) but the bottom line is that, all else being equal (athleticism, height, etc.), the DB begins the play at a slight disadvantage to the WR he is covering, and the disadvantage only widens as the play goes on. The inherent disadvantage isn't an "excuse" for poor coverage or technique (and we have had our share of that as well) but your defensive gameplan needs to account for it.
I don't think our secondary is that bad. They ain't good, but they're not that bad either. We have had our share of blown coverages, accidents (DBs running into each other, slipping, biting on play action, or just getting out-techniqued) but they're not as bad as some might suggest they have looked.
We simply need more pressure up front to force the QB to make bad throws. Our DBs need to improve their technique as well (and we do have a good DBs coach in Jon Hoke) but pass coverage is very much tied to QB pressure, and we're not doing our secondary any favors right now. It's simply not fair to expect DBs to cover as long as we repeatedly call on ours to do so.
This in part goes back to playcalling. The reason why the Steelers and Patriots own Peyton Manning year after year is not because they start 11 Pro-Bowlers, but because their Xs and Os consistently put their defenders in a position to make plays. Manning isn't that good when he's hurried (not many QBs are), he isn't mobile, and the Steelers and Pats consistently take advantage of that with aggressive blitzing and tight man coverage, forcing him to unload before he wants to.
Right now, Richard Smith ain't giving us good Xs and Os (and yes, I recognize that the Steelers D is more fundamentally talented than ours, but the talent differential isn't nearly to the extent that our scores would suggest.) And if he doesn't start doing that, then our secondary is going to continue to look bad.