[NYCAP123]

Another reason for the higher salaries on yachts is the lack of job security. Yacht crews deal with very finicky personalities; a bad mood (yours or theirs) and your job (and maybe your career) is gone. Whereas in the commercial trade what matters is getting the job done. Throw a hissy fit at a crewmember from a tug and watch what happens.
As someone else mentioned, we are also jacks of all. I'm just a small boat captain. We don't have engineers, but I wish we did. You have no idea how much it's worth to have one person taking care of your yacht. Every outside hand that gets into it is trouble, especially if you don't have someone representing you over his shoulder. As a small boat captain I've got to earn my years salary in 7 months, but be available and on call everyday for 12. When I'm out I have to navigate, pilot, troubleshoot, act as personal security, make emergency repairs, act as laison with the yard, maintain a list of competent jobbers in every trade, keep the boat clean and oh yeah keep smiling and be charming at all times.
And yes we charge more because our employers can afford it and they don't respect anyone who doesn't value themselves. If you analyzed most of my employers jobs based on the amount of work they perform they'd be worth about $10 an hour. That's not what they're paid, because that's not what they're worth, and it's the same for their crews.
Of course, if it doesn't matter if your engineer shows up drunk or hung over or not at all or tells you guests to stick it I'm sure you can find an engineer who will work quite cheaply. Just decide what you want to pay and I'm sure you'll get exactly what you pay for.