The only justification for the late pledges I can see is about knowing what financial position you'll be in when the money is taken.
I pledged on day one for a 9-car DCC set, then upped it to an 11-car. Right now that's a scary prospect, as I've had a load of unexpected expenditure come my way since. I may have to scale it back, but I'm desperate not to do so unless we reach the funding goal regardless. That, and I'm sure the short term pain will be worth it in the long run...
Still the last week has seen a good surge, and if it does continue then it's looking not at all unlikely.