Indeed, permitted but not recommended, I guess I should have looked at the RFC itself. The fact remains that a lot of devices that ought to support TLS 1.2, break when TLS 1.0 is disabled.
As an example, see this test result for my own blog. Amongst the carnage is Android <4.4.2 (my phone is 4.1, have talked to ZTE about this), IE 8-10 on Windows 7 (doesn't affect me so much, but big corporates, this is a big problem) and Safari on MacOS X <10.8.
Now if it were a site for my own purposes, sure, I'll crank the security settings sky high and to hell with browser compatibility. TLS 1.2 is no problem. However, I can't control what the general public uses, and this is the sort of trade-off that a commercial business trading on the Internet has to make.