Doesn't using a freight forwarder solve most of the mentioned problems? Seller keeps their PayPal protection and buyer can use whichever shipping method they choose. There is a small additional cost which they buyer can judge worthwhile or not.

Having said that, I find asking the seller to ship OS will generally result in a positive response.

eBay is geared toward the buyer and unless the shipper uses a tracked and insured service it is very easy for them to be frauded.

I'm not sure people get so exercised over this. I was going to say it's a free country but of course ebay isn't a country, although it's turnover is higher than the GDP of many small countries. Anyhow, sellers can sell to whoever they like. Many people just want a nice straightforward transaction and can't be bothered with customs forms etc.  Although, as has been said above, if you have good feedback and ask the question many sellers will agree to ship to the UK.

excuse me sir - i dress very nicely with nothknkg brutal about my apearance. i like the old brooks broterhs style that Johnny Simons sold back in theday. Its all a bit wateted down now and a bit to moddy for my tastes and his shirts only fit teenage boys but i still like Johnnys shops. Aerly Ivy DShop and early JSimons in covent garden well then johnny had some fantstic gear for sale then. Real top notch threads that anyone who knows anything about clothes loved so so much.

Seriously, some of these issues remain - but it's not confined to Ebay.  Dig the stateside bookseller on ABE who wants in excess of £50 to ship you that Louis L'Amour paperback you failed to buy on a market stall for 10p because you'd spent too long in the boozer. 
Send a message to Warren Harding-territory in these hard times you'll be lucky to get a response.  American sellers, on the other hand, can be a positive delight.

^ LOL!