They don't seem to care - I've seen companies on .org
The way it was SUPPOSED to work:
.COM - Companies/Commercial
.ORG - Organizations - at one point, implicitly nonprofit
.NET - Specifically related to Internet provision/support/service etc.
I believve there are more rules applied to some domains, like ".BIZ" and a few others.
There have also been some breakups, like the ghastly "New.net" (spyware) and others that offer additional TLDs.
http://www.opennic.unrated.net/
http://www.open-rsc.org/
Because ICANN, the "offical" administration have shown themselves to be dithering and incompetent, many alternative TLD's have sprung up - in many cases, they do make some effort not to duplicate ... logic would have dictated a straight alphabetical split, into as many or as few groups as would faciltate management. It's time the old order shaped up or shipped out!