Onto this idea of "poor drafting" if you go Manning...
first, in a traditional league, I wouldnt take Manning in the first and he wouldnt be there in the second. That said:
(1) Projections - everyone lives and die by projections, then feed it in vbds and all that jazz. Well, wth do projections REALLY mean? A guess? Seriously - we know that 1/2 the top RBs wont be, that guys get injured, or lose their position, or a combo of the two. Projections seem to be a pretty "optimistic" viewpoint.
When you have a very very good chance of getting an advantage by going QB, and a slim chance of striking gold, decent chance at doing good, decent chance at doing meh and sizeable chance of bust with a RB?
When you then take into account the next points about why you can veer away from the traditional thought that you must go RB and that VBD or whatnot tells us there is no value elsewhere.....
(2) How other guys draft
If you know that you can get two RBs that YOU think have a very good chance to do well, or better than well in the 2/3/4/5 rounds, hey - more power to you. Lets face it, there is a good amount of shuffle year to year. If you can pick out which guys rebound, or come from know where, or are just undervalued/underated and drop, then it is pretty smart to take another position (be it QB or WR) and go RB later.
(3) Points over the competition on a week to week basis
Once again, we focus so much on lists, and sheets and projections at this time a year.
In a week, we will be talking about THIS weekend. What player "x" will do against the Bears defense and should I start Samie Parker or Matt Jones. Or, one or the other could be hurt, or lost a slot on the depth chart and those projections over a year are rendered useless.
Consistency comes into play. The chance of my players to outcore your players on an individual and group basis. If I can get a QB (or WR) that I know will help me win fantasy football matchups each weeks.
Before my ramble goes on TOO long, let's just say that there is more to winning fantasy football games and leagues than projected numbers which assume no injury (for the most part) and really lose a lot of meaning for different reasons, when looking at week to week fantasy football realities.
And of course, if your draft will lead you very good value at RB later, and you have a chance to gain an advantage elsewhere, it seems prudent to do so.
Sorry I dont have any charts to back that up.