I'm a physics student. I'm not:
- a programmer
- an ethical hacker
- Anything that has to do with chemistry
- Anything that has to do with robotics
- an electrical engineer
yet I have a good amount of rep on those sites. Take a look at Rory Alsop and Gilles as well.
Similarly, people on Christianity.SE are not necessarily Christians. There are a lot of folks who are active on multiple religion sites (the mods of these sites are a good example)
People on Politics are not necessarily politicians.
The sites have some experts and a lot of enthusiasts. There are enthusiasts who know a good amount of stuff about the topic, and there are enthusiasts who are just interested in learning. This means that the type of person varies a lot, regardless of rep.
You'd be measuring apples here and labeling them as oranges.
However, take a look at this SEDE query (you can compose your own if you wish).