This has always been the model of MVNOs. They are wholesale customers of the carriers. Usually the carriers put them in a one-step-behind technology (Straight talk didn't get iPhone till later, Straight talk didn't get LTE till very much later).
Even though they have it now, there are noticeable differences. ST forbids tethering, streaming, etc. AT&T doesn't care what you do with your data. Straight Talk doesn't have visual voicemail, and since it's not an official carrier, the experience isn't as seamless as ATT. Nonetheless, it's the same network.
And yeah, I realize there are ways around several of the issues, so stop piping in telling me I'm wrong. For the average user, you pay less but you're getting less, be it customer service, or technology both fall short compared to ATT's direct buying experience.
But for the price it's a BARGAIN!
Thanks! It makes more sense to me now.