Racking Up Stats, or Secretly Great?

Spurred on by the BS's (Bad Sunglasses) post the other day, I was glancing around Pro Football Reference, which, with it's counterpart Baseball Reference, are a wonderful, Christmas-morning type sites for anyone with a modicum of interest in stats. Anyway, I was glancing at the career leaders in a few categories and kept seeing names of players I knew were good, but would never have guessed them to be anywhere near the top in any major category.

I'm talking about players like:

• Curtis Martin, 4th all time leading rusher with 14,101 yards. I mean, I guess he was good. I always remember him being there, but I never remember him being that good. Could be that I lived in the far reaches of the West Coast during his run (no pun intended), but he just kinda quietly racked up a whole bunch of yards for some generally mediocre Jets teams (and a couple solid but not great Patriots teams).
• Jerome Bettis - see also Martin, Curtis. I have pretty similar feelings about Bettis, who clocks in at 5th all time with 13, 662 yards. I guess I have more respect for him, cause he had to haul around that hulkish frame of his to get all those yards, which is pretty impressive, all things considere.
• Dave Krieg - 12th all time leading passer, 38,147 yards. This guy... I tell you what, he led my fearsome Sea Chickens to many a 9-7 season... I would hazard a guess that most of the people in Seattle, where Krieg got the lions' share of those yards, would have a so-so to negative impression of this guy. Sure, I was young at the time, but I seem to remember him fumbling or getting sacked constantly at the worst times of the game. But even he is in the top 15 of ALL TIME, PEOPLE!!! He beats out such luminaries as Steve Young, Phil Simms, and BS's favorite, Troy Aikman.
• Larry Centers - 13th all time leading receiver, 827. First it bears noting that after Jerry Rice, it's a rather precipitous drop off in this category. That being said, a frickin FULLBACK???? On the one hand, you're glad for him, cause obviously he got to be more than the glorified mobile lineman that fullbacks are. Don't get me wrong, i love me a good fullback. Shaun Alexander doesn't rack up his MVP season a few years back without Mack Strong knockin guys down in front of him... It's just that Centers is now ahead such HOFers as Steve Largent, Michael Irvin, James Lofton and Charlie Joiner.

Fundamentally, my question on players like this is always whether they were really that good, or whether they just piled up stats by being mediocre for a really long time. I think thus far the Hall of Fame has done a pretty good job of weeding these statistical freaks out, but it's gonna be hard in the coming years with all the crazy stats people are putting up year in and year out.