Verizon licensed the C Block in 2008, which come with rules that REQUIRE it to allow any phone to run any app. Unfortunately the FCC has been gutless about enforcing the rule. It took the agency 10 months to force Verizon to allow tethering apps in Google App store. If they'd had any guts, they would have banned Verizon from selling the 4G iPhone which, as a locked down phone, is arguably illegal under the rules.
In fact, Google argued that it would be illegal for Verizon to sell a locked down phone on that spectrum, but then once it started to need Verizon, it refuses to stand by its earlier rules.
And these rules matter a lot, because come spring, a federal court will rule that the FCC's net neutrality rules have no legal basis and the ONLY net neutrality rules left standing will be the ones on Verizon's C Block.