There are several reasons for the shortened lifespan of new rams.
1. They are a short-lived fish anyway, usually only averaging around two years.
2. A lot of LFS rams are farm-raised fish that are hormoned before export to really boost their colors, and hormoned fish often have shorter lifespans. It happens in discus, too.
3. Rams do not handle stress well, and being moved from exporter to LFS to home aquarium in the span or a week or two is a lot for them to deal with.
4. As mentioned, rams are best in warm water, 82 - 85F, and they may not do well for extended periods of time in an LFS that keeps their tanks in the mid 70s.
5. Rams do not like dirty water, so frequent water changes are preferred. They do best in low nitrate/low DOC water. Not all LFS do frequent water changes on their overstocked tanks.
Basically, with rams, if you take an easily-stressed little fish and put it into a community system with sub-par water quality that's too cold, it ends up being a recipe for disaster. I often see them covered in ich at my LFS. They're susceptible to all sorts of things once they're stressed out.
The best suggestion I have is to find someone who is breeding rams on a small scale and get good, healthy stock directly from them. A lot of discus keepers also keep and breed rams because they love discus conditions -- warm water with frequent water changes.