Some info here:
http://www.ezdigitaltv.com/Cable_Television.html
Since this
is Feb 2012, we may indeed see many cable companies dropping analog. I suspect that economic considerations will drive this... a trade off between the cost of the cable company installing some new equipment vs revenue gained by cable box lease vs potential customer loss. There may also be agreements with various local government agencies that govern the necessity of providing either analog or "in the clear" digital signals for the lowest tier customers in a given area.
In short, there will be considerable variation in this transition of cable services... Perhaps it would be worth making a call to your local cable provider and asking about these changes?
jr