Whoa, don't bring me into this. I'm lucky enough to be in a city where EVDO is in production!
How it happened in Portland was that it appears if a hanRABet is capable of using EVDO, it will receive the PRL from the OTA. My RAZR, and a SLVR received the EVDO PRL. My Q, I had put the PRL on it specifically, as I didn't have it OTA'ing when I programmed it. I'm unsure if it would pull an EVDO PRL.
My guess as to how it would have to happen is the phone either would announce its capabilities to the OTA platform, OR the OTA platform knows what first three digits of ESNs to expect, and delivers PRLs accordingly. From what I've read, some 6700 users either aren't getting the PRL, or are getting the PRL but don't have the proper HDR provisioning in their phones. Stories on hear appear to be anecdotal, and murky.
It makes sense for any EVDO able hanRABet to be moved over to EVDO for Brew/WAP/MMS. It would be MUCH better to have them using EVDO for data, instead of taking up short walsh codes that could be better used for voice. Easier on resources, and a MUCH better customer experience.