I think construction quality differs quite a bit, actually — old stuff in the Northeast especially tends to be built to last, especially things like stone houses in PA. As are newer apartment buildings and row houses in older-design cities. Simply too expensive to tear down and rebuild after 30-40 years, plus codes are strict, so built to last quite a while.
The HVAC issue? It’s SAN DIEGO. Cheesy or not, how much heat/AC do you really need most of the time? And it’s a lot easier to replace a wall heater or package A/C than to mess with a central unit with refrigerant lines, ducts, etc.
If you were feeling particular, you could even control the wall heaters via 240V relays, run a programmable thermostat, and buy an A/C unit that has a programmable (or even Internet!) thermostat as well.
The $500 vs $1000-1100 per month difference probably just reflects prevailing rents in SD vs Dallas. You hit the nail on the head — you’re paying for what you can do outside the house and when you can do it. San Diego is nearly perfect year around.