You have to put a trap on the ac drain in some counties around here, even if its positive pressure. I'd prefer not to have them, lots of service calls with a plugged up drain for no reason. Now it's different if its draining outside or on an air handler but I'm just saying your typical basement install it's silly. imo
We still do about 15% of our installs as 80%ers. We have a lot of oddly constructed century homes around here where venting a 90 is basically impossible. AFAIK we are required to trap every job around here whether it needs it or not (except with drain pumps, sump acts as trap). One city around here (Broadview Heights) requires an air gap in the drain line.
We are in Phoenix, and we have a hard enough time getting people to even replace their furnace, more less going to a high efficient one. They get turned on for maybe 30-50 days a year max, so there is little pay back. 95% of our replacements are 80% furnaces