For the techies its a good deal to shop elsewhere but, for the general public its nice to have everything done for them at the store aka Set-Up + Go , they probably don't do that at costco. I'm sure people will be sent to verizon to have screen protectors put on, gmail accounts setup, email setup, and demo's of the phones.
It's really a shame that verizon does that to its own employees that try to make a living off of selling these top-selling devices when places right around the corner sell devices much cheaper then send them to the local verizon store to have them finish setup process.
I don't blame any verizon employee for not wanting to help a 'verizon customer' setup a new device, that did not shop at their store. just my .02
If you plan on just getting a good deal on phone/accessories and setting up everything your self by all means go shop where it's the cheapest just don't expect great service if you bring your device over and say hey I just bought this at "so and so" and they didn't transfer my contacts.