It is in the chipset, but the operating system has to show it as an option if you want to use it. You can't put a ubnt card in the mikrotik and then get access to functions that definately exist in the card if mikrotik doesn't make those functions a choice.
If mikrotik removed wds from the choices, it would still exist as a function of the chip... you just wouldn't be able to use it. Same goes for repeater.
hmm, if that is true, why would MT than not just enable that extra functionality in their ROS. It would give them a great sales point, won't cost them anything and actually I see no setbacks for them in enabling it. So I don't know if it is that easy.... or these guys are a bit ............
As proof that this is a function inside the chipset: "Some devices that DD-WRT works on do not offer the repeater mode. The DD-WRT firmware has it as a choice, but not all radio chips support it." That right there is proof that the repeater function is a feature of the radio, not just the software.
However... even on the radios that do not support repeater-mode, DD-WRT let's you put the radio into client mode AND you can put a virtual AP on the same radio at the same time... making a working repeater on chips that don't even support it! So, even if some chipsets prevent it... it is still possible by putting the radio in client mode and adding a virtual AP.
Unfortunately, Mikrotik does not give repeater as a choice, even on chips that support it... AND they don't allow you to use a Virtual AP on a radio in client mode. "Virtual AP only works on station mode." So, Mikrotik stops both methods from working, the hardware mode and the software mode.