So this is Sony's strategy to win November NPD

Thankfully I just got a tutoring position, and have since quit Wal-mart - where I was a cashier. It would've bothered me to see people do this. I honestly don't care if it hurts Wal-mart as a whole, what I care about are the people who work for Wal-mart it can hurt, and also the gaming industry in general. Not to mention how the company is working for the consumer by price-matching and certain individuals want to take advantage of it to the point where the costs of doing this exceed the revenue and Wal-mart decides to stop. Sorry socialists in this thread, this is not a good thing for the consumer, in fact it will probably hurt the consumer much more than it will hurt the producer (Wal-mart.)

Wal-Mart deserves every bit of it.

It isn't about ignorance. They tell us to just match the price. For a price-difference this large, the store manager would have to approve it. This probably happens once or twice per store. The manager would rather just give in, because there is a reputation he needs to uphold of price-matching everything. Now there isn't much loss (we call it "shrink") when it happens to one store, but if it happens to many, and if it gains momentum it can become a problem for not only Wal-mart, but its competitors, the consumer, and the gaming industry. Just as you said, it weakens consumer rights. 

Imagine the November NPD numbers now with 89$ PS4s!!!

The PS4 was likely to sell-through its shipment anyway. What this will do (if it had such a significant effect on NPD numbers) is create loss for the company (Wal-mart) and they won't order as many shipments in the future (assuming they keep their online price-matching policy.) For a console like the PS4 that means fewer sales, not more. Supply is the biggest issue for the PS4, not demand. 

I'd do this. No shame at all. It's not like Sony will miss the money. I guarantee you only a handful of individuals in the world are doing it in the first place. There only losing out on a few thousand dollars, which is pennies to them.

Does Walmart pay for the product in full before they receive it from Sony?

One thing for them to give 20% off an item, but that is 80% off the price. How could a store not have exceptions in policies to avoid situations like this?

Yep. I've heard stories of customers bringing an Emerson TV box with a broken beat up Samsung television in it and the managers forcing electronics associates to take it as a return. Then the customers looking smug that they got their way. It is ridiculous. But somewhere in the cost-benefit analysis for either the store or the corporation as a whole it is worth taken this loss and keeping a certain reputation. Walmart stores indirectly compete for bonuses, and managers need to make sure their store doesn't take a big loss even if it would save the corporation as a whole a lot of money just so the employees can get a decent bonus. There are just so many factors, and even in the manager's case he/she probably is able to figure out that it is fake, but make a decision against denying the return because it could cost even more.