The wiring is somewhat more complex, I can attest, after spending an hour staring at it making sure he wired it as a mod and not a quasi-mod furnace controlled like a single or double stage.
I get the feeling that 90% of HVAC work consists of customers asking "can you do it cheaper?" and **** long-term costs of buying an 80 versus a 90+ mod.
Since most HVAC units are purchased by the people who DON'T pay the energy bills (building contractors and rental owners), why would any installer be familiar with the good stuff?
I also get the impression that linear increases in wiring complexity result in logarithmic increases in installation mistakes.