I suppose it also depends what you are paying for and if you feel that is worth it.
I've been looking at Cervolo's, amazing frames, the R3 being on the Paris-Roubaix podium means that in standard guise it's as much as most people would ever need, and definitely more bike than I'll find the limits of! The designs are all from Canada but the carbon laid in China with the quality control being maintained by Cervelo. Those are the bikes that the race team use...however a lot of the research into new bikes and manufacture is done in a special plant in California. They now produce a small number (one per week) of frames by hand. The frame is 300g lighter than the Chinese production line one (albeit a hand made production line and already under 1kg) and hand prepped and formed in the design plant. The frame then costs almost triple! Does it ride better, the pro's say yes. Would the average mortal know...no. Can you race the bike from California? Not without adding close to 300g to it to make it legal!!!
The point is what are you paying for? The hand made top of the range bike with cutting edge technology. Tech which was only available to the race teams but as some people wanted it they can now buy it. Most people do not care about those last few grams of weight saving, eating one less burger is much cheaper for most of us, but some people can afford it and do want that state of the art machine. The same tech does trickle down to a more mortal price point in future years. Look at Di2 and now Ui2, I suspect next year will have a 105i2! It all depends on how long you are prepared to wait...for some not long if they can pay now.
Peoples hobbies are also different. For some the latest golf clubs, memberships, travel to courses round the country and golfing paraphernalia run into many thousands. Others take flying lessons and buy a share of an aircraft or hundreds of pounds per hour in hire. Track day motorcycling costs thousands with trailers parts and race tyres which are worn by the end of a weekend not to mention the bike itself! There are countless hobbies and pastimes where a one off payment of £8000 that would last years may seem very good value.
It doesn't make an £8000 bike cheap or for some remotely justifiable, it does however need to be put into context of what some are willing to spend on their hobbies, pastimes and sports!
Pete