Do iPhone 5 devices come pre-loaded with the latest firmware (IOS 6.1.3)?

I went to AT&T store just recently and got an iPhone 5 (I took it back… Don't judge me), and when they activated it, I'm not sure how but it already had 6.1.3. (Which I do not want.) I'm now wondering if all iPhone 5 devices come pre-loaded with the latest firmware. Or if that is just with places like AT&T and Radioshack. If not I want to try to go to Walmart if that will make a difference. I'm starting to feel like they just push it through. But I prefer not to have the latest update… (if possible).
so let me know…

It's whatever is in stock. Let me guess you need an older firmware for some stupid jailbreak that will be obsolete in a few months.