I can't believe no one put this in qualitative terms on this supposedly 'objective' or 'engineering' oriented forum.
I would say high end simply means the top 5 or even top 1 percentile. This could be defined by price, or inversely by the number of customer who would buy it, or by a formula that mixes price and target market size. (Obviously, a very small company with no marketing can't be called high end just because they don't sell many units.)
Qualitatively, objective sonic performance is important up to some point. From there, other factors, such as materials, craftsmanship, aesthetics, services become progressively more important. As the price goes further up, other factors such as individualized services and the ability to customize the product will come to play. These factors are probably much more important for high end speakers than anything else in the audio chain, because they are often big and they interact with your room. Heck, even B&O came to my house and put together a pair of Beolab 28 for me, and they don't even break the $20k mark.
All this is to say that, the more high end you go, the more the manufacturer would bend over backward to make you happy.