'Thriving countries' is not the same as the proportion of 'tax-take' from the top earners being generated. The Speccie published some tables a while back using KPMG figures and I have just looked them up.
In the first one you can see a comparison of the top rates of tax and how they have changed.
Interesting as you mention Skandinavia to see that Sweden has slightly reduced their top rates while Norway has increased them though not as much as the UK.
Here below is a chart showing the impact that changes to the top rates of tax have had over the years in the UK.
There is current evidence that the impact now of the 50p rate is even greater and more immediate. The reason being that those hit most by this are much more 'mobile' now than ever before and can very easily transfer to lower tax regimes.
As I say the choice is between a cosmetic political top rate of tax to satisfy the masses or a lower top rate that will help provide a high tax take gain for HMRC to help deal with the deficit.
I do agree that it is difficult to reduce the rate. Going along with the lowest common denominator argument and keep the 50p rate is the easy route but is that also the most sensible? We have a deficit that needs dealing with and it is important to get more growth and increase the levels of tax revenue received by HMRC and that means reducing the top tax rate.
Personally I prefer them to do the right thing and to go out and make the argument for it. I am sure most people will be bright enough to see the sense. A few masochists may choose not to do so and there will always be the class warriors of course, but by arguing the case these can be marginalised.