The Certitude is Breathtaking
Take a look at most if not NFL rosters, and you'll find a lot of guys you never heard of (Way to go, Peyton Hillis)!
What it all boils down to is that, when it comes to the draft, there are no set rules. (There may be probabilities that pan out more often than not, but there are plenty of exceptions. Guys like Hightower get drafted as late as the 5th round and guys like Steve Williams and AJ Jefferson don't get drafted at all).
What does that tell you? It tells you that, if you pass on Adrian Peterson in favor of Levi Brown, you bet wrong.
But, just as easily, Peterson could have gotten injured as expected and, who knows? Levi could have played LT on Day One and turned out to be All Pro. Or not.
You rolls your dice and takes your chances.
I think the correct approach to the BPA vs. Need issue is that the best you can do is be "site-specific" - i.e. to look past the ratings/numbers and dig down into what makes either of two choices tick. Sometimes (though not most of the time), your gut might point to the needs-guy over the BPA.
And even then, you won't always be right. I do believe that, in the long run, if you follow a BPA/Value philosophy, you'll be more right than wrong and will gradually raise the over-all talent on your football team to a higher level than if you usually put need over value.
There's a political dynamic in play here - If you're a GM, you can afford to follow a philosophy that gradually strengthens the overall value of your roster, but if you're a HC, if you bypass need in order to strengthen the overall long-term talent-level, you might be building a terrific team for your successor.
But back to fan-certitude. If Bill Belicheck were drafting for the Cardinals, we'd be trying to lynch him. He fills all those extra picks he gets mostly with guys you never heard of. Yet his teams are perennially in the playoffs. Maybe he and other guys know something about football and maybe we don't know as much as we think we do.