well let's use at&t for example i remember on my lumia 900, I couldn't use it as a hotspot because it said I needed to contact at&t I bought a random unlocked one becausei live in the Bahamas and it wasn't available here at the time I just assumed at&t locked that feature. I could be wrong and that might be another issue but i was just mostly wondering about which final version of 8.1 i would get since i had the DP version running.
Ah yes, the good old Lumia 900 hotspot issue. You are right. That was one of those things, although it too was just a configuration issue. If I remember correctly (I'm not in the U.S.), AT&T wanted their customers to upgrade to a specific plan (which was usually more expensive) if they wanted that feature activated.
Anyway, just know this:
You can think of the OS as being identical for all devices. Everywhere in the world. On all carriers. In that sense there is no difference for any of us. There simply is no "carrier version" of the OS. The version of WP that you get through the developer preview will ultimately be the same version that you will get through your carrier. If you already got the newest version through the developer preview, you won't get that again through your carrier. The developer preview is distributed earlier, but otherwise there is no difference. What does differ is the firmware.
The firmware is built by the OEMs, who usually assemble a custom firmware version for each of their customers (the carriers). The firmware also contains the OS configuration files.
If you have a Lumia device with AT&T 'flavoured' firmware, you will eventually get the updated AT&T 'flavoured' firmware too, whether you've opted into the developer preview program or not. After that happens, there is no difference between a developer-preview device and a normal device.