This is an interesting discussion, and is actually quite complex. The principles that MMM writes about will apply to nearly anyone, but not everyone will be able to do what he has done. MMM is very smart, had a higher than average income, has a deep understanding of efficiency and delayed gratification, has a spouse that is in high alignment with his visions, has excellent health, etc.
If you are earning a below average salary and have other confounding factors you will not be able to replicate MMMs success, but what he teaches will still apply to you. Increase income, decrease spending, invest the difference. As evidenced by some of the replies above (and other threads) people are doing some pretty incredible things at low incomes and complicated situations just by applying the principles of the blog.
What we are really talking about is inspiration. MMM resonated with me because I could relate to him. Some people will not be able to relate as well, but there is a reason this blog is so popular and others like it are not. The good stuff rises to the top. There are other people writing about this stuff at all income levels, but for whatever reason people want to read MMM more. Jacob has written the template for extreme frugality and retirement on a very low income. Anyone wanting to retire on a low income needs to read all his posts. All the information is there. There are millions of frugality blogs that dive into the tactics of living on less.
Increase income. Decrease spending. Invest. That's it. Take what is useful from these blogs, discard what does not apply. I do think that complaining about the fact that his income was higher or he writes off blogging expenses is ridiculous. Throw that stuff out and the basic bones of what he teaches still applies.
I would also say that this is an opportunity for someone with a low income to start blogging about early retirement. Sounds like a business opportunity to me.
TL/DR: Read MMM and ERE. Understand the philosophy. Supplement with other tactical frugality blogs. Stop wishing there was a blogger that is more like you and have gratitude that guys like Pete give us this stuff for free.