Right now, the NFL is setting records for passing yards and RBs are being marginalized somewhat. Despite this, RB still rules fantasy football drafts in the early rounds, with most players drafting both their starting RBs in the first two or three rounds.
I kind of see the reason why. Every year there are going to be a couple of RBs who put up monster fantasy numbers that no WR could ever hope to match. The problem is, which RB will it be? Last year it was Charles and McCoy. The year before that, it was AP, Martin, and Foster. The year before that, Rice, McCoy, MJD. And the season before that, Foster was the only RB to score well above the top receivers.
Point being, everybody that picked a top 3 RB the year after his big season has been at least mildly disappointed the next season every single time, and in some cases those picks turned into huge busts as RBs are prone to get injured and miss time.
The other thing is, sometimes a RB will just fall off the face of the planet. Look at Ray Rice and Doug Martin last year. Really every season you have a few RB who went from top 10 to outside the top 25 the next season.
By comparison, the very top WRs tend to be a bit more steady. Calvin Johnson has been money in the bank 3 straight years. Demaryius Thomas too. Jimmy Graham might be better than both, as he's consistent and puts up monster production compared to an average TE.
There are going to be a couple of monster RBs every year that are going to have significantly more points than the top pass catchers, this is true. But for all the other RBs, their point totals are going to be roughly in line with the top WRs, except that the top WRs have so much less risk.
I think a lot of people go RB-RB because they think there aren't enough RBs to get good ones later. This is kind of true if you draft normally. What I did last year was wait until the 5th round to get Reggie Bush, who I correctly believed to be a breakout player, and then I stocked up on RBs, using my entire bench for nothing but RBs and WRs. I think I had 5 RBs.
During the season I churned through these RBs getting new guys who looked like they had a chance to be high workload guys. Most of these moves didn't work, but ultimately it doesn't matter how many failures you have, only how many successes. One of the players I received using this method was Knowshon Moreno. I also got Zac Stacy and narrowly missed on Eddie Lacy. Moreno finished 4th, just barely behind Marshawn Lynch, and Bush finished 11th. Stacy would have been a top 10 RB if you prorate his numbers over 16 starts. Lacy, who I could have had but was too slow on the trigger, finished 5th.
So even though I avoided RB early, I still finished with one of the better RB groups in my league. All while having by far the best WR corps (Megatron, Josh Gordon, Andre Johnson, Vincent Jackson), Drew Brees at QB, the best non-Seahawks defense and the league's #5 TE (Witten). My kicker was just waiver wire du Jour. I used this method in both leagues and finished #1 in scoring for both, in one league it was a bit of a blowout with #2 sitting almost 200 points behind me.
Now, you could do this same method with different priorities. For example you could go RB-RB early and then load up with a zillion WRs and work the waiver wires. The only reason I don't like that method, in addition to the anti-risk argument stated before for taking RBs early, is that it is much harder to discover breakout WRs than breakout RBs. WRs can struggle for years before breaking through, whereas RBs tend to hit their groove within their first couple seasons. And since RBs can tend to rise quicker and fall more precipitously, this creates a perfect storm for new blood to excel at the RB position every NFL season.
Also, RBs that are a product of the system tend to fly way under the radar too which is why I was able to get Knowshon Moreno off of waivers.
Add to this the fact that teams are increasingly looking to dump veteran RBs for rookie-contract youngsters, and it really shouldn't be any surprise that in recent years there have been a ton of "surprise" RBs in fantasy.
Why take big risks early when you get excellent production at RB by churning through the less heralded guys, knowing that any one of them has a fairly decent chance of being the next surprise star, all at zero risk and zero cost. Even if the odds are a little low, all that means is that you just need to churn through a lot of prospects, churn through enough and you are very likely to get the 1-2 hits you need.