I don't think thats the reason at all, i'd say thats more the fact they are harder to register than a .co.uk or .com etc... to register them they need to be the exact match to the companies registered name or the registration gets rejected, this has stopped the abuse that other TLD's have received over the years.
I was looking for answers based on actual experience of working with the domains, but thanks anyway.
www.autogas.ltd.uk seem to do ok seeing as their link profile isn't that impressive, with only a tiny 68 linking root domains!
