[maxerickson]

It's not that eccentric. For instance, Marx didn't look just at what the job involved but at the terms of employment. In his terms, programmers making some of the highest salaries are still working class because they are paid a wage by a corporation. A plumber operating a business by would be middle class in the same system (they are working for themselves).

There are ways in which those distinctions are much more interesting than wage levels (which tend to dominate "class" discussion in the US).

[emodendroket]

Well, Marx has more nuanced categories than just wage earners and capitalists. The professional class doesn't have class interests that are identical to those of manual laborers.