Thanks, this is depressing, but at least appears factual. The Verizon rep. at store started with telling me that the phone internals are different for VZ and other U.S. carriers (which I know isn't true for at least ATT & Tmobile, only the Sprint SKU is different because of the difference in Sprint's LTE bands), so it appears that this unlock prevention is software enforced.
http://www.extremetech.com/computing/166356-iphone-5s-and-5c-the-best-support-fo r-3g-and-4g-lte-networks-worldwide
What I'm surprised by is that Verizon has done this blocking even for phones bought at full price - so they have just resorted to their old ways (after their welcome departure from it with the iPhone 5), I guess. At least they are leaving it unlocked for overseas carriers and not forcing roaming charges on you - something to be thankful for.