Nil,
The situation you describe at GLA is a very rare one and something I have never done, nor witnessed, an ATP can go 1 min behind a 737 on a TRN departure whereas the 737 needs 4 mins behind ATP.
I can only assume one of 2 things happened tehre:
1. You had a slot and were early
or
2. A trainee in the tower made an incorrect decision and justified it by stating that ATP taxied first so departs first.
Definitely not the norm as I'm sure you're aware if you operate into / out of GLA as frequently as you probably do if you fly for the orange crowd.
Feel free to come and look at our antiquated equipment anytime you like, we might even be able to find a chocolate biscuit.