The Corsair AX series do - they have a hybrid mode to turn the fan off at low loads.
How do current-limited wire groups differ from separate rails?
Only if PSU's temperature is below certain limit.
Put it into 50C ambient and I bet fan starts about instantly regardless of "user controls", if not that's very bad design.
That's the amount of fan control every credible PSU would give user.
(looks like Antec Earthwatts Gold Pro lost that)
Go count number of fuses in fuse box.
You wouldn't claim utility company has that many power lines coming into your house, or would you?
Similarly those "separate" rails are nothing but marketing BS.
Actual independent 12V sources would have major extra component costs and space requirements.