Not necessarily are they allowed to work in the UK. I agree with you - I think working should be possible at least as I firmly believe there is great benefit to Turkey in allowing non-nationals to generate business. It would take away the obvious jealous tactic when a non-national is generating wealth, the phone call to report them for working illegally. Success helps more than just the owner, the area and taxman also benefit. Not allowing people to work (under regulated conditions) does not protect Turkey or Turkish workers, it does exactly the opposite - it stunts growth and strangles opportunity.
All that said, this action is to stop the use of tourist visas by full time residents. I think that is the correct thing to do. As I have said previously, I do not agree with the cost of residency permits for Brits in Turkey. I became sick of hearing expats telling anyone who will listen about how much they "support the local economy" by buying Efes and bread; like they were the saviours of Turkey. I do however think it would be unwise to overcharge Brits for residency as they do spend and boost the local economy in many ways.
It is important to know who is resident in Turkey from abroad and the residency permit is necessary for that reason. Perhaps a no fee residency permit is the sensible way forward.
My comments, by the way, about cheaper council tax than the UK were not made to imply that cheaper council tax was a reason to live in Turkey. The point I was making was that although residency is an unwelcome cost, people can often lose sight of the overall tax/expenditure comparison.