Keith
I'm not looking at the bigger picture because I fail to see one. I know a lot of ex Bristol students through my FTO, and others from attending the brush up courses. The vast majority passed their exams first time and every single person was more than satisfied with the tuition and support they received. I have never met an unhappy ex BGS student.
Bristol have deservedly built up a reputation of being a good school.
I am not suggesting that the other ground school providers are in any way inferior to BGS. They do seem to get more good press on these pages than any other school, but that good press is not without foundation.
What is it about BGS students that makes them more disposed to make posts? I can only suggest that it is satisfaction with Bristol's product, coupled with the fact that there seem to be more requests for opinions on BGS than most other schools.
If you receive good service, you tell people about it. That is all that is happening here.