Google has great customer service, in my opinion. Their support specialists are well-paid in comparison to their counterparts and generally more knowledgeable. However, this is my opinion. Take it for what you will. I've used their customer service for non-Nexus related problems as well: problems with accepting payment on the Play Store; problems with my Gmail account; and problems with my Play Music subscription.
My parents still go into the store to buy their phones. And then they leave, because the store never has the color and storage configuration they want. Two-day shipping has changed the game. Already you have carriers catering to online shoppers (e.g., Sprint's new delivery program), carriers offering online-only discounts, and I think you're only going to see this grow.
I'm not saying that people aren't shopping in the stores. I think, especially around the holiday season, people are eager to go into their service provider store. But the frustratingly long waits, uninformed customer service, and unavailability of products has made shopping in store relatively inconvenient. It doesn't justify the drive or train over anymore.
And honestly, most people either want the iPhone or the Galaxy. If they're shopping for another phone, they are likely very informed and know what they want. Why not take the carrier store out of the equation and just ship the damn thing!