The difference is that if you go to, say, Best Buy, and buy a Samsung TV, a Sony Blu Ray player, and a game for your Wii, your personal information doesn't go to Samsung, Sony, and the Wii game maker. The store, Best Buy, gets your info, not the makers of the products sold in the store.
This is what people generally expect from stores that sell a variety of items from many different manufacturers.
What makes you think the first sentence is true?
I would in fact, assume the exact opposite.
I've bought plenty of things where the warranty was automatically registered by buying it at best buy, and samsung/sony/whoever sent me a postcard, to my name and address, letting me know that.
It's very clear my personal information was shared.
The thing about Google Checkout is that it's more of a "credit card processor" than the merchant. They consider the developer as a merchant (maybe because Google might have first designed Google Checkout to be payment processor, like Paypal) which basically makes transfer of goods between a customer vs. developer, as opposed to customer vs. Play store.
Aside the argument if it's good or bad, it seems to be consistent with that notion -- if Google is considering Google Play to be more of a promotion service with payment processing built-in, as opposed to curated content store.
