George Your answers on Page 72-41 Chaper 3 (3-4) 1999 NFPA 72. Most nowadays are Class B Class A requires the outgoing and return conductors to be routed separately and shall Not be run in the same cable assembly. Page 72-41 (3-188.8.131.52*(Note exceptions) on page 74-42
Depends on the type of buildings you work in. More than 50% of the building I work in are Class A due to reliability requirements and occasional slow repair cycles. Many are not familiar with Class A circuits and they are not specified due to "that's the way I always did it, and it worked that time"
Most of our systems use class B, where you see 2 jumpers in the panel per zone and 2 wires going out. Class A is safer because it can be cut in the middle of the loop and still cause an alarm on either end. A class B intelligent system may not use EOLs because each device is polled so you don't need a resistor, capacitor, or diode at the end to know that you're getting to the last device.