Google is crafting buzz like Apple is doing with the queues at the Apple store or their irritating "reserve your iPhone" that in reality does not reserve anything. A difference though, if you don't want to bother, you can simply order online and it get it delivered the old boring way once it is back in stock. The Nexus can only be bought online.
(disclaimer: a bit bitter after having tried to buy a Nexus 4 today)
They could just as well have component supply problems.
They could also want to control the amount of unearned revenue on their books.
Not exactly difficult.
I can log in to any bank and it'll tell me within a few moments of when a charge was made.
No you can't; that's exactly the issue. Most people don't know the difference between an authorization and a charge. What you see on online banking as "pending charges" or "holds" are authorizations. No money has moved hands -- your bank balance has not gone down, the merchant's bank balance has not gone up, there's not even an in-flight ACH somewhere yet to be processed.
Literally all these entries on your online banking represent is a message of intent from the merchant to charge that much to your card in the near future. Even your bank does not yet know if the merchant actually captured the funds and they'll be settled (the money will move) soon or if they only performed the authorization. They could void the authorization or let it expire itself without ever charging the card.
Hence the comment -- even if Google only performs an authorization, it looks to the customer like they paid, and the bank won't tell the customer otherwise. That makes using authorizations to hold preorders untenable from a customer service standpoint even if it were technically possible, which it really isn't due to the short period authorizations are valid outside the hotel, travel and rental industries.
The fastest your bank could possibly show a charge I make to it right now is tomorrow. Most will take longer than that. If it's near a weekend, it could take 3 or more calendar days. The authorization can show up immediately, the charge cannot.
Authorizations happen in real-time over the card networks. Settlements, where the charges get recorded and the funds actually move, happen in daily batches (or even less often).
In the meantime, customers assume they have paid for something, because they see it in the pending charges or holds list, whether funds were captured or not. Again, refer to previous comments on why that makes authorizing cards for the full amount of preorders problematic.
If you're running a brick and mortar store, you want to serve the customers who are there now. That means not cannibalizing your inventory by mailing to someone who ordered last week. You also want people to come back to your store.
It is irrational for the store to mail you one when it comes in stock, though they should have a web-based corporate distributor that they can direct you to.