That is partly true. I don't believe there is XML code naturally supported for FSX, much less FS9, for a supercharger switch. You must write your own code to get it to work and unfortunately I am not that well versed in XML code - I can make any slew of movable levers or clickable switches, but most of them are left at that.
When people talk about full systems modeling, it rests on having someone that is a master at XML code, and certainly module files, and finding work-arounds to get items to provide certain results based on what FSX gives you. Items such as a working supercharger and hydraulic hand pump is on the list of items I'd like to work on creating, though it will take some more learning first - like most of this work, it isn't all talent and skill, but mostly knowledge of what to do and experience doing it. The supercharger switch itself, if left in auto as usual and is assumed that it is within the product, will not have to be manipulated, as the supercharger will adjust automatically depending on altitude. Between 20,000 and 20,500 ft, the supercharger high blower light should turn on, but doesn't - this is something that will definitely be addressed in the update.