I'd wager the reason that Apple is listing a bunch of the AT&T and T-Mobile MVNOs like Cricket and MetroPCS in with the Verizon/Sprint phones is because those customers buying them are more likely to want to switch carriers, specifically to Sprint and Boost/Virgin Mobile. Apple doesn't want to deal with the anger that results when someone finds the $700 iPhone they bought (or, worse, had to chunk buy out from failure to understand how this whole money lending system works) won't work on the cheap carrier they've now picked thanks to failure to pay bills and targeting advertising. They're already on a low-cost carrier, and more likely to run into a StraightTalk or Walmart-like MVNO using any number of the Big 4, including using CDMA. I'm giving Apple the benefit of the doubt here: I think it likely they really ARE thinking of their customers here, being pro-consumer.
Long and short: don't buy a Sprint iPhone. Buy the Verizon model if you're playing this game, the FCC mandated their "unlock". Sprint is a terrible company, and if you get a locked iPhone good luck on getting them to unlock it. Truly, a place in Dante's Hell for the people who run that company. Also, good luck taking a CDMA phone TO Sprint, invariably they'll tell you that they can't register it, even if it is clean. They want to lock you in by selling you a locked phone. See prior point. (Verizon has come far on this issue, surprisingly.) Really, just don't use Sprint. Just don't. Their network sucks and their plans are that cheap because they're desperate and they're hoping you're stupid. Seriously. I can't stress this enough, DO NOT BE A SPRINT CUSTOMER.
(For the record, I'm NOT a Sprint customer. I had been a very happy Sprint customer, however, about 20 years ago when they first rolled out digital service. I was never personally unhappy with them. I despiiiiiise AT&T. LOATHE THEM. But I've watched how the modern Sprint treats its customers and how it advertises; at least AT&T is willing to SHOW YOU WITH THEIR LOGO that they're Darth Vader. Sprint is just shady, definitely Emperor Palpatine, Darth Sidious. And though I despise AT&T, I'm on their network. Because it mostly works, has significantly better coverage in my area than T-Mobile, and the price is much more reasonable than Verizon. I'll side with Vader over Sidious any day. "The enemy you know." Oh, and perhaps ironically, resale value of locked Sprint phones is crap at the trade-in services, but surprisingly high on Craigslist. Who'da'thunkit?)