@A bit slower here
> So why does the UK have to wait until 2012 for it all to be completely rolled out?
We could have planned to "just flip the switch". It might even have worked technically (i.e. after the "big bang" rollout the signal may be good); it would certainly have been a lot easier technically to plan. ("Turn off analogue and old-low-power-digital then turn on new-high-power-digital" is easy; any other transition plan is really hard because you have to avoid interference between old and new). But from a pragmatic point of view it would cause serious practical difficulties:
1) The plan is that in each region, BBC2 analogue gets switched off first, and a limited digital service gets switched on*. Then 2 weeks later the rest of the analogue channels are switched off, and the rest of the digital channels are switched on. This gives people 2 weeks to check that their digital reception works, and there's an easy "can you watch BBC2" test. It also means that failure to be ready isn't a big deal (you just lose BBC2), people can go out and panic-buy during those 2 weeks. Additionally, because digital is available they can and do put really annoying permanently-visible scrolling warnings along the bottom of every analogue channel saying "this is an analogue channel and will stop working in a few days; call this number for help!". This all gets lost if you go for "big national instant switch"; people just think "my TV stopped working" and don't know what to do about it.
2) One of the taxpayer-funded organisations has a digital TV helpdesk that you can call for help; there are also other support efforts that are run e.g. by Age Concern. With a "big bang" you'd have to predict demand, train a _lot_ of staff, and most of the calls would be in a 2-week period. With a region-by-region approach the peak is smoothed out a lot - so you need less staff; they will be more experienced (cos they've probably done a few regions by the time they get to you); there will be the right number of staff on (because the managers learnt from the first few regions); etc.
3) How many digital receivers should the shops have in stock for the mad panic-buying rush around the switchover date? Before Whitehaven, no-one knew. As regions gradually switch then the retailers will get an even better idea. (Whitehaven was the 1st region to switch).
4) There's a limited number of staff for all this. Support people who go around and help old folks; Sky installers (some people do switch to Sky); Aerial installers (some people do need a new aerial (or aerial cable) for Freeview); call-center staff; transmitter technicians; people to troubleshoot the transmitters if it all goes titsup; etc. Doing region-by-region is a lot easier.
5) If it does all go wrong; the damage is contained to a single region. Also, lessons learned from the first few can be used to improve the switch of later regions. (Incidentally, I'm told the reason Whitehaven was first and London will be last is for technical spectrum allocation reasons. Apparently it's nothing to do with population size at all, that just happens to be a happy coincidence).
(Disclaimer: I work for a company that makes Freeview boxes; but I speak for myself and any errors are mine)
(* Yes there are plenty of people who can't get Freeview but have a perfectly good analogue service; switching off analogue without turning on new higher-powered Freeview transmitters would annoy a _lot_ of people. And you can't up the power for Freeview without annoying lots of people with interference, unless you turn off an analogue channel (such as BBC2) and reuse that frequency for digital).