I think that, to a large degree, it's like any other learning curve. Unless you fight your way out of comfort zones, refuse to let the bozos upstairs define you and pigeonhole you, and change jobs as soon as you're at a dead end, you will plateau after 10 years, most likely... and be obsolete after 10 more. I don't think that it's inexorable, and I think that some (but sadly, not all) of the 45-55 income drop is voluntary (once the kids are through school, they downsize their houses, only have to pay 2 airfares instead of 4-5, and since they need less money, work less).