High end 1911s usually have better no non-sense warrantees, have fancy finishes on them, use forged frames and slides, use tool steel parts, and put a crazy amount of man-hours into fitting the parts (and the people doing it are highly trained and require a higher salary than normal manual labor at lesser shops). The more expensive guns will have match barrels and bushings, they'll have checkered front straps, they'll generally have more options so you can actually customize the guns to your taste, and often they will offer accuracy guarantees. Also, you won't need to consider replacing a lot of the factory stuff, like springs and grips and sights. Oh, don't forget bragging rights, exclusivity, and generally awesome re-sale value.
Honestly, you can buy a very good 1911 for $1000 and be fine, but if you have to ask the question of "how is my $1000 1911 not as awesome as a $3000 custom?" you probably won't understand.
FYI, the new Mustang GT offers awesome performance for $35k, why do people buy $100k Porsches? Get the question you are asking now? If you've never driven a Porsche, you'll likely never understand.