Do you know in Logic 9, in the mixer, that if you instantiate a multi output plug-in, that it will add a little plus sign at the bottom of the fader, and that when you press on this plus sign, that Logic will make a new aux with the next available individual output that plug-in has available to Logic?
It is now an automatic thing... so, to answer your question, the plug-in is the "device" that defines how many outputs it shows to Logic, not Logic.
In Logic 7 one HAD to create an autoload to that they would have all the necessary tacks, aux, bus, and instruments required for a song. It was a massive pain if you had to0 add even 1 of these parts to a new song. Now, you need a track to make one, and Logic dynamically creates it, if you add a bus Logic adds a new return, etc. it is a much better way of doing thing, unless you are a composer who has a huge amount of instruments you need, and then you can still create a template. I feel that the new logic 9 method is a much better way of doing things in the end.
Does that help you understand why things are different, and how they work now? It IS a drastic change, and as a long time Logic user I love it... but it did take a while to get my head around it.