Well, let's break it down. What made you think that speaking at conferences and being an author made you much money? It's rare for speakers to get paid unless they are speaking at world-class conferences (and even then it's not a lot). Also, book deals do not earn a lot of money, even those that sell hundreds of thousands of books only see a small fraction of that money go to themselves. The people that stand to make money in publishing is the publisher, because they've done all the work.
Typically, the best-paid designers are either contractors with a proven track record over many years of designing key businesses, or figureheads in large businesses that again have proven track records and have designed products that have been highly successful.
You say it's a limited skyline, but what fields don't have their limitations? Programmers don't get paid much unless they work in finance or in mission-critical fields. Doctors and Lawyers have high earning potential, but again many of those earn very little at the start of their careers, gain huge debts along the way and most don't end up earning much more than other "thought-workers". Even accountants are never guaranteed to learn a lot of money, especially those that want to work on interesting accounts or want to work for themselves. Chasing money is fun, but ultimately if you're not doing what you're doing for the fun of it you'll burn out before you make your money.
The assumption of riches in the web seem to come from the very rare stories of those with no experience in building sites striking lucky. It's very common nowadays to see beginners wanting to design and develop sites in the belief that they're making a career for themselves. During the dot-com boom every jackass that could code some HTML thought that they were developers and were deserving of some of that sweet cash. This low barrier to entry is why many designers and developers aren't paid nearly as much as they should be, both for the level of education they hit and how valuable their skills are to businesses.
Those that do make their money make their money for themselves.