Per the smell/temperature issue - there is a crucial factor being left out:
Lack of humidity. Humidity tends to spoil, Aridity tends to mummify/desiccate.
When I first came to AZ, one of my kids left a slice of turkey in her room and somehow she didn't see it and forgot about it. It didn't smell. At all. It turned into jerky, basically. This would not, could not have happened in NY. It was strange. Also, citrus (unless in a plastic bag) and pomegranates will harden and dry out if not eaten up. They don't smell. Liquids evaporate.
This could have been something of a factor in the roommates not detecting a smell in the first couple of days perhaps. Granted, a decomposing body is not a slice of turkey or a pomegranate, but the smell may not have been as apparent due to the low humidity - until maybe day 3 or 4 - with a closed door and an indirect route to the shower, the air may not have moved that much.
I don't understand why anyone is doubting the roommates on this issue... (?). I think if they had smelled something that concerned them, they would have investigated it. Apparently they didn't. I don't question their statements about this. Det. Flores knows this smell, and recognized it immediately. Had Travis not been found then, the roommates would have likely found him soon enough. They may have become accustomed to the smell - or figured it was garbage - or something coming from outside.
I certainly don't think they're being dishonest about this... They didn't catch on. That's about all there is to it, no?