This is actually not true. You still can deal with a Verizon store, especially if they are a corporate store. If you buy the phone from Amazon, Best Buy Mobile, or anywhere else the fact is that you are a VERIZON customer. We have had issues at Best Buy Mobile when customers come in after the first 30 days.
Verizon has no record of where you got the phone, and to be honest it is none of their business if they ask. They do have record of when you got the phone, so that's enough for a warranty related issue.