If it works, use it. Like the other folks said, a lot of phones are left unsupported by their providers with no official updates. Then you have the choice of using it and not worrying about the OS, as long as it works right. That's fine for the average user who isn't likely to do a lot of USB-to-computer interfacing with it to do the upgrades or mods...
But if you really want updated software you can look into things like Cyanogenmod. Doing that got my unsupported phone all the way up to Android 2.3, whereas Motorola left it languishing with the only supported version at 2.2 or .1
2.3 has been doing well on my phone for awhile now, but if the Cyanogen guys put out a stable 4.0 release for my phone I'll definitely try it.