I would venture a guess what triggered this was problems in the DTV coupon program.
This program offers each household up to two coupons. (in the form of cards, similar to a debit card) Each coupon could be redeemed for US$40 off the price of a digital receiver. Digital receivers are selling for around US$60-65.
The coupon program has more or less run out of money. "more or less" because they're finding many, many coupons are being ordered but never redeemed. They do have an expiration period. (90 days) I suppose the theory is that if the analog shutdown is delayed, more unused coupons will expire and more money will be available to issue more coupons and more viewers can use those coupons to get converted in time.
That said, most Americans are more than willing to pay more than $60 every month for cable or satellite service, it seems unlikely that a one time payment of $60 for a converter box is going to be a problem for most families.
(for those families for whom $60 is a problem, I have sympathy... although they really should have acted sooner...)
There is also some concern that viewers in some places are having trouble receiving all the channels they were getting in analog. Problem is, in many cases that's because:
The digital signals are suffering interference from analog transmitters.
Or, they're having to operate on reduced power to avoid interfering with analog service.
Or, the station plans to use its current analog antenna for its permanent digital service -- is currently on a lower interim antenna -- and of course cannot switch to full power until it can turn its analog transmitter off.
Of course delaying the analog shutdown only delays the delivery of a full digital signal to these viewers!