Because that is more of a bus protocol where the physical connections are common and each device is given an address. Then the master poles each address and only that device responds. It saves you having a stupid number of UARTs or trying to bit bang multiple instances which will appear to work for a bit but will fall over if it gets any degree of traffic.
Seems logical.. will explore this.. However
RS-485 would mean adding a small MCU like a PIC or AVR to each sensor, though, unless the sensor has an MCU already that can be modified.
This could be a problem. Having 17 mcus 
Sounds a sure recipe for a lot of chaos.
Hehe the first OS I remember is Windows 98 Grin! Ah man I feel really young now..
Well i really started with DOS but then i wouldn't want to count on that as all i new was cd, md, format a: & del*.* (the last one was special i used to modify a bat file to run del . on the school computer!)
So you really are young, I started with a main frame and punched tape.
how was it? always wondered how these systems booted? and what people actually used them for?