Fwiw, this is definitely possible. I've saved about 80% of after-tax income for the last decade or so in SF. I don't consider my life very ascetic either; in fact, it's pretty awesome. If I wanted to cut down further for some reason, the number of wonderful free/cheap things you can do in popular cities is insane.

(Though bear in mind that I'm not yet in the phase of life where I have a kid, where this stuff gets a lot more complicated)