The history to this is that Nominet has (now) got a voting structure which favours the larger registrars. Members (registrars) get votes somewhat proportional to the number of domains they have registered, this means the top few members effectively influence the UK namespace to their financial advantage.
The "need" for the .uk rollout has been pushed by those members who will benefit most from it. There have been a couple of consultations on this and many smaller members (as well as members of the public) have put forward strong objections to the rollout and some have suggested alternatives as it has been clear for a while that some rollout would happen. It should be noted that there are members of staff at Nominet who are very unhappy with this being pushed through, although the executives seem to be happy given they are on performance related pay.
The draft proposals that Nominet came out with (twice) were roundly rejected at the consultation stage; although they could have chosen to continue with the poor suggestions they have chosen to go with one of the most acceptable ways in which the rollout could happen. It's a classic case of offering something terrible in the hope people won't complain too much when the next offer is just poor.
If a rollout had to happen then the easiest way would have been for an automatic, no cost, redirection of .uk to .co.uk addresses - but this did not provide revenue. What we have is a situation where there will be confusion and additional cost but in the long term .uk will be seen as the commercial extension for the UK and .org.uk will remain the non-profit. All other UK extensions are almost being ignored for this, although there are circumstances where they could be offered the .uk
As stated above by another member, this should have happened a long time ago. It is happening now though and I think that we will see some big companies switching for two obvious reasons (amongst many others):