I spent far less than $80k to get my degree from a big state school in the US, so this doesn't necessarily apply to the OP's situation if indeed that's the minimum they'd end up spending in the UK.
But I have to disagree with you that it's a "gigantic blatant lie." Perhaps it's overly optimistic regarding the quality of education one would get for $80k, but it's not a lie. Sure, you can get very well-rounded by reading books on your own but there's a tremendous amount of value to be gotten from going to college too, maybe even a different kind of value, or for a different person.
I took a fair amount of higher level math in college and I really don't think I would have had the same experience studying that stuff on my own. I'm sure there are people who can read abstract algebra, analysis, and geometry textbooks on their own and get 100% of the understanding a good professor would try to impart during lectures, but I bet they are rare. In 16-18-yr olds, probably quite rare.
Regarding liberal arts courses, I had the opportunity to study Japanese literature and film with some really great professors, and that's something I could have obviously done on my own (watch movies, read books, write critical papers and mull over them by myself). But it's not the same. Maybe not better, maybe not worse, but I disagree with your assumption that self-study is a drop in replacement for college.
"Doing a startup" probably offers a great deal of opportunities for personal growth and well-roundedness, but I really don't think it's going to be the same as studying things like upper division math, compilers, the French new wave in depth at a decent university class.
I completely agree that college is totally over-priced. At $80k, my arguments start to look a little flimsy. But as a blanket statement, I have to disagree with you that the idea that "college offers value to someone wanting to be well-rounded" is a blatant lie. Also, your tone was a bit shrill.