They may be becoming more consistent, but I started with BT applications testing in 2001-ish, and stacks varied significantly.
Also, carriers have significantly impacted BT functionality. Verizon prohibits file transfers from taking place, and that led to wholesale OBEX problems for a long time. So it is conceivable that carriers no longer influence the BT implementation, but they have in the past, and I know of NO reason to blithely assume that it has completely stopped...
I get the feeling that you think like an engineer, and I think like the guy who has to make it work after the engineers build it.