Well, SOME of Decatur is on I-65, but it's a rather rural area. Get off the interstate and you'll find the rest of Decatur.
Also, Charles, Decatur has its own industrial base. Here's a sampling:
http://www.mceda.org/default.aspx?id=47 and
http://www.mceda.org/default.aspx?id=46 . Most Decatur residents don't work in Huntsville. Some do, yes, but a very small percentage.
What's holding Decatur back is our schools. We have had a heavy influx of Latinos over the past 10 years - legal and illegal. Most of the children come into the school knowing NO English. Just in the past couple of years are the teen-agers actually staying in high school long enough to graduate. We have a couple of elementary schools where English is spoken as a native language by less than 20% of the student body. So, you have teachers having to teach the kids English before they can even begin to teach reading, writing, arithmetic and all the other stuff that schools have to teach now.
The fact that we are still under an integration court order more severe than Huntsville's does NOT help. We can't build a school or change school attendance zones without federal court approval...and they take
years to approve or deny anything. So you'd better choose your residence location carefully, to get into the right schools. Of course, that's true everywhere.
It wasn't always like this. Our schools used to be rated second only to Mountain Brook's.