That used to be the case, but in 10.7 they changed the green window button from being "zoom" (snap the window to fit its content) to "fullscreen". They let you change the default behavior back to zoom for a few years but seem to have gotten rid of that setting. You can still access the zoom behavior by option-clicking the green button, but on basically every program I've tried, zoom just means "maximize" like on Windows now. The only exception I've found is Preview, where "zoom" seems to mean "make the window take up most of (but not all of) the screen and scale the image up to some random value". One image I tried got scaled to 146%, another got scaled to 207%. I would think it should mean "scale the image to 100% if it's smaller than the display resolution" but who knows, I don't work at Apple.
Edit: Finder still has the correct zoom behavior, it's the only program I've found so far that does.
The behavior of the (now option-clicked) zoom button is actually determined by each individual program. Most stock apps will either fit to content or toggle between the last two recent sizes, but a lot of third party apps (especially those built with foreign UI frameworks) tend to turn it into a maximize button.