Offensive lines are important for mediocre quarterbacks. Time in the pocket will allow even the worst quarterbacks to thrive, and no NFL secondary can hold up for 20 seconds on end. So clearly from a pass protection standpoint, quality offensive linemen are worth paying for. But when you have a good quarterback especially a good quarterback that recognizes tendencies before the snap, this goes out the window, at least when talking about offensive tackles. A good quarterback who understands his offense and protection scheme can compensate for a poor offensive line to a certain extent. If you want to see a very detailed explanation of protection schemes at the NFL level, follow this link to see former Green Bay Packers RB Paul Ott Carruth explain these schemes. It's a great read for anyone interested in the X's and O's of NFL football, it'll also make the point I'm making more obvious.
What you can see in the link above is the amount of flexibility and responsibility quarterbacks have in determining their protection packages. For young quarterbacks and poor quarterbacks, the center is usually responsible for the exact protection calls. That's what Jeff Faine did in 2009 for Josh Freeman, but the young quarterback took on that responsibility in 2010 and did a good job. In addition to that, Freeman understood how his defense worked and where everyone was at any given time in a play. The result was that his sack rate dropped dramatically: in 2009, Josh Freeman was sacked 20 times in 340 dropbacks, or 5.9% of the time. In 2010, he was sacked just 28 times in 570 dropbacks, or 4.9% of the time. That's with a worse offensive line, too. So why, exactly, does this happen?
First, Freeman understood where any free rushers would be coming from because he set up the pass protection, so he could avoid free rushers with his legs or by getting the ball out quickly. More importantly because he understood his offense, he knew where he could get the ball at any time, he understood all the hot routes and could check in and out of plays to avoid particularly bad situations. All of this combined to make the offensive line less relevant as well: Freeman needed less time in the pocket to complete balls and could coordinate with the offensive line to compensate for any weak points.
But it's a bit harder than just making offensive linemen less important. Obviously you still need competent linemen, because a pass rusher in a quarterback's face withing 2 seconds is always a problem. Even Peyton Manning struggled at times this year because his protection was simply terrible. But the Bucs have competent tackles: Donald Penn is a good tackle, and James Lee is a good enough pass protector to produce with.
The interior O-line is a bigger concern, though, for two reasons: first, the quickest way to get to the quarterback is up the middle, and a poor interior O-line will allow quick pressure up the middle, preventing a quarterback from stepping up. All of that is killer. Second, the Bucs don't really have great players at guard and center and this hurt them last year. Ted Larsen is not a good player right now, although he could turn into one. Davin Joseph had a surprisingly poor year, and replacement Derek Hardman didn't do much better. Jeremy Zuttah and Jeff Faine were both serviceable as centers, especially in pass protection, but neither is a standout. Poor offensive tackle play can be compensated for, but it's a lot harder to do so for interior linemen.