I also read it a long time ago... apparently it didn't stick with me much.
What you describe in your first post sounds like accounting for a business, more or less. I think that's good advice, and I'm surprised that more people don't look at it that way. But, the idea that more money will solve the problem is limited advice, IMO. Wasn't RDPD in sales? If you're working on commission, the solution to financial problems might be as simple as to "sell more". I see personal finance as more like the whole business, and not just the salesman. Imagine you're a CEO of a public traded company during a recession. People aren't spending money, so "sell more" just isn't an option. How do you maintain (or raise) your stock price while sales/income are stagnant? You find other areas to trim the fat. It could be a matter of lowering expenses, re-evaluating the cost of your product, evaluating market demand of your product/services (and remove unprofitable ones), taking people off payroll, etc.
Comparing that to personal finance, I think it's no different from cutting spending, making a teenager get a job to pay for their own car, downsizing a house, evaluating if you're getting paid what your skills are worth, finding ways to increase productivity (or gain time) but make the same amount money, or evaluating other job options. In the end, it's all about net worth, and there's a lot of different ways to get there.
I think MMM focuses on decreasing costs (vs increasing income) because he was earning a fairly high income when he started. There's a lot of resources out there about how to bring in more, but not near as much about being efficient with what you have.