I co-wrote Pro VB 6 & XML, back around 2000. I was lucky; it was a topic I (at the time, at least) knew fairly well, and a good part of what I wrote was based on a project I was actually building at my Real Job. There was some time spent researching technical details for the W3C XML DOM and VB this and that, but overall I think the time O spent for the money received worked out quite well.
So you might that that was a good thing, except, being my first real writing job, it gave me serious misconceptions about making money as a writer.
Not too long after that book I contracted with Wrox to write Beginning Ruby. Long story short, it was tedious and painful and I got next to no money before Wrox went bankrupt. Even had they not, and had the book been completed and published, I seriously doubt the time/money ratio would have beat simply getting a job as a waiter. The tech book market had, at that time, turned to crap, and Ruby was barely a blip on anyone's radar.
A bigger issue was that such a book required far more technical research. Basically, it meant a lot of work to ensure that what I wrote was actually true.
I've done assorted writing since then trying to be more careful about picking assignments, but it's not often like that first time.
That's not to say people can't or don't make money writing tech books, but it really helps if a) you can write with authority without having to keep looking stuff up to verify accuracy, and b) you manage to hit a sweet spot in timing and audience interest.
(Or, c) you don't give a crap about the quality of your work and happily pump out drivel that gets past shoddy tech reviewers prior to publication. Please do not do that; there is enough of that already.)
It's very sad for the publishing industry. If they cannot find a system that allows authors to make a reasonable amount of money, they're not going to last long considering that it's much more convenient and less stressful to just publish your book online, if you're gonna do it for free (and is just as good for your reputation if you do it right).
I've made a reasonable amount of money from my book, and it's not all that popular. It wouldn't qualify as full-time work for me, but since I've written it I've had a steady stream of additional income. No complaints.
I'm sure he'll make plenty of money consulting, but to see so much sweat for minimum wage, ouch.