I think that anytime there's a close enough competition to where the younger, cheaper, up and comer can take over the role and save precious cap space in the process, it's going to be seriously considered.
Vereen 2013---47 catches for 3 TD's (missed 8 games) 4.7 yds per carry
Woodhead 2012--40 catches for 3 TD's (missed 0 games) 4.0 yds per carry
At this pace, (and I hate to project) it would be quite reasonable to consider Vereen to have completely blown away Woodhead's 2012 totals. After all, he already caught 7 more balls than 2012 Woodhead in only 1/2 the games played. On top of that, the running production didn't suffer one bit, aside from the fact that it was unfortunate that Vereen broke his wrist.
As much as people tend to complain about these moves, the ones they tend to complain about didn't really seem to hurt us nearly as badly as what is normally insinuated on a daily level. Our problems weren't with losing Woodhead, Mesko, or Welker. None of them... Our problems were in having a murdering star TE, another star TE who is useless in our 3rd consecutive postseason in a row, severe injury situations up and down the board, and the fact that we were forced into using 3 rookies at the position of WR. Most of all, it was likely with our defensive losses to the heart of the other side of the ball with Wilfork, Kelly, Mayo, and Spikes.