I believe most retailers such as Best Buy, Amazon, etc. require you to sign their own contract as well as Verizon's. It usually doesn't mean much other than having an additional ETF if you cancel within the first 6 months. As you noted though, they often have great prices for older phones (Radio Shack has the Incredible 2 for free with new/renewed contract right now), but newest phones are almost always the same prices everywhere.
Also, I don't know if this applies to you, but if I understand correctly, only Verizon Wireless will let you get an upgrade price with an annual upgrade option, if you still have one of those. For example, I got my last phone on November 18, 2010 (before Verizon discontinued the annual upgrade ~January 16, 2011). Therefore, I am grandfathered into the annual upgrade option and can get the upgrade price for a new phone (might have to pay $20 more though). If I purchased a new phone from Best Buy, Amazon, etc., then I would have to pay the full retail price until my 2-year contract expired on November 18, 2012.
Incidentally, if I wanted to upgrade to something like an Incredible 2 for cheap retailer prices, I would be out of luck. Again, with one-year upgrade option, I can ONLY get upgrade price at Verizon Wireless. That was probably a lot of information that you didn't even ask for!