That's the thing. We can't possibly know who would or would not have been available later in the draft.
We, and the Kiper crowd, see the draft as almost purely a hierarchy of perceived "talent". This guy gets a 2nd-round "talent" grade, whereas this other guy gets a 5th-round grade. So, a guy with a 5th-round grade should be selected in the 5th round. If he's actually taken a couple rounds earlier, then we assume that it's a significant "reach" and the GM is either a genius (if it works out) or an idiot (if it doesn't) because the prospect certainly would have been available later - according to his "grade".
The fact is though, probably 50% (or more) of what determines when a prospect gets picked is the perception, on the part of the GM, of the demand for that prospect's services by other teams (the draft is essentially an auction, after all). So, if the GM really wants a specific prospect and he's certain that the prospect will be off the board by his next selection opportunity, he has to take that prospect right there and then (even if it's a couple rounds "early"), regardless of what we (or Kiper or Mayock) think about the prospect's talent level.
We simply do not have access to the information about potential demand from other teams that BB does.
This is all much easier to see with the jockeying for position/line-jumping in the 1st round, but it happens in pretty much every round. In fact, a major reason for teams trading up for what turns out to be a bust is "irrational exuberance" for a given prospect's perceived talent on the part of multiple teams. To a great degree, much of the expectation that a prospect will be taken in the 1st is often the result of publicity, that sometimes borders on propaganda, combined with a serious tendency toward group-think and oneupmanship on the part of team owners that blinds them and GMs to red flags that a more dispassionate evaluator would take into account.