In my experience, it is NOT valid in general. If you simply go out on the marketplace and say, "Hey, I'm a good hacker, give me a contract job!", then clients will calculate your worth by taking the $80K figure. (Clients are much better businessman than you are, much better negotiators, and usually need you much less than you need the contract.) But, you won't have 8 hours worth of work per day, so you'll go broke.

The trick is to be more than just a general-purpose "hacker". You have to be a "Security expert" or an "iPhone SEO expert" or an "Oracle DBA"... The trick is, you have to know a market segment, and have a good understanding of what the business value of your skill/work is, and then you can charge based on that.

And of course good networking, good people skills, good self-management skills, etc. Stuff that "hackers" usually don't care about.