Unfortunately with customer service, especially via emails, you are dealing with very low-level employees that aren't making it a career to answer customer service emails. The ones that last a few months are probably moved up into better positions. I had one job where the majority of new hires don't make it beyond 2 weeks! (I was there 3.5 years, so I got to watch that revolving door quite often!)
It can be questionable if the email is read at all. It could be some program that scans the email for key words, thinks it knows what you are referring to, and automatically sends the response. And even if the email is actually read, they'll probably getting tons of email. They aren't sitting back and closely reading them. They probably have goals or quotas they have to hit, so lengthy emails aren't going to get the time needed to read it all...especially if all you want is a free night or some Hilton points.
Now, think of the posts on these boards when people say they've written emails. Almost every single time, the responses tend to say that the OP has provided way too much information not related to the issue. I'm kind of thinking that this goes on way too often. Email responses that have nothing to do with the issue seem quite often related to something written in the original email...which had nothing to do with the issue as well!
So...do shorter emails = better responses?