Of course people can change their lifestyle. I have no doubt that MMM and the extreme early retirement guy, and some of the devotees of those blogs, have done exactly that.

That doesn't mean extreme frugality is the first thing people should focus on though. People have limited willpower. Using it to cut out $20/week worth of lattes or $100/month worth of cable just isn't the best use of it, unless you've already covered the more important things. As I've tried to illustrate above, focusing on the wrong things (and failing), can be very counter-productive. Personally, I think your limited willpower is almost always better spent adding to or honing the skills that will allow you to produce more.