I think as a general rule (and someone else said this too) that American amps are fabulous, whilst the UK is much more competitive in speakers. For example, ProAc and PMC are known and respected by audiophiles across the US, and both companies have received glowing and detailed reviews in Stereophile. PMC just signed a distibutor agreement with an American company; I have a friend who just spend big money on ProAcs to go with his all-American system. On the other hand, some of the leading amp companies in the UK (Leema for example) don't even bother with the US market. Others are available but barely known (Roksan). Naim and Linn are well-known, but viewed as being very quirkily British. The US amp market is really strong. McIntosh, Ayre, Creek, Mark Levinson, etc. are tough competition.
I think the problems that the OP alluded to in the US have a lot to do with the sick state of retail in general, though the dominance of home theatre is a factor (Americans are a lot more likely to have the extra space to make into a HT). Independent shops in every industry are on the decline, being battered by internet sales on one side and the onslaught of the mega-stores on the other. The shopping experience in America is so unbeliveably superior to the UK: the service, choice, hours, return policies, and prices are better. But the downside of this is that it is very difficult for small shops to compete. It's great that one can buy pharmacy items 24/7 from ten different big retailers, but imagine the impossibility of opening a small chemist's shop in that environment: it's impossible. There is no way to compete on hours, price, etc. So most small retailing has moved to the internet in a way that has only just begun in the UK, and the physical shops available are either mega-stores (who can survive, theoretically, on volume) or ultra-premium boutiques (who survive thanks to big margins). A midrange shop just can't compete with Best Buy or webshops on volume or on the cost of doing business - so they are gone.
My parents live in Florida. In Orlando, a big agglomeration of two million people, there used to be five or six traditional hifi shops. By the time of the financial crash, there was one, which was put out of business by downturn. There are some upstarts there now, but all have a 'home theatre and custom installation' value proposition, with little apparently in stock.
This is typical of modern American retailing, not just hifi. The incredible inefficiency of the UK retail market (and the relative - for now - immaturity of the UK online market) has ironically resulted in more smaller shops and choice (again, for now - I see all the same trends happening here as usual).
In the meantime, if I were buying American hifi (or rather, buying hifi in America), I would do what every other American does when confronted by the tyranny of big-box shops: buy it all on the internet. You buy it, audition it, and then send it back if you don't like it. Is this more convenient? No, but it's what you have to do these days. At least you are auditioning in your living room.