As Weaselboy posted, unless MSFT has a secret arrangement with Amazon, GameStop, or other gift card retailers, they won't know what is bought as the code issued is specific to those sites and acts as a regular gift card.
Well, I hate to say it, but... they do have that arrangement, at least indirectly.
Those gift cards don't come from the retailers. They come from a benefits clearing house that many large corporations including mine use. This clearing house also stocks the gift card kiosks you see in major retailers from Lowe's to Walgreens. The one I am most familiar with is "Exclusively Yours", aka "EYCARDONLINE", aka "myprepaidcenter.com". I'm sure there are others. I'm not certain who is behind this one, but if I had to guess, I think its American Express. Thats just speculation though, so don't run with that.
A company may want to start a program that rewards workers for good attendance, for productivity, sales, what have you. They invite one of these reward clearing companies in to structure a program for them. Rewards consist of points that can be spent at dozens or hundreds of different retailers, plus the option of taking the points as a gift card. When the worker spends the points/card or gifts them, the multiple faceted tracking I described in my earlier posts takes place. The information gathered by your transactions has an enhanced value, because the points company knows where you work, your employer provides demographic information about you, and can (CAN - I'm not saying they all do this) offer a general or even specific idea of what your compensation package is. I'm not privy to the kickbacks that the employer gets, but I'm thinking that they get a significant discount on the points cost, while there is probably some kind of expense structuring going on so they can claim the entire reward "cost".
With the Bing Rewards program, Microsoft doesn't have a direct relationship with the card
issuers, but they do have an arrangement with the clearing house that processes the cards, which gains them the same information. Its similar to your bank issuing a VISA card. They don't clear the card - VISA does, but both companies share in the information gathered. Its not a scam, but a brilliant way for companies to actually get paid for giving rewards to workers. Its actually the next logical step after store loyalty cards, which of course I don't participate in.
*Helpful hint: You really don't need to sign up for a "free" account to get loyalty discounts from most chains. When you're asked for a loyalty card simply say "Please use the store number" or "Please use the manager's card". Just about every chain store out there keeps generic member club cards or pendants near each register, and will use them in lieu of a registered loyalty card when asked. Obviously, this doesn't work for paid memberships, like the Barnes&Noble discount shopper club (do they still do that one?), and ymmv, but it doesn't hurt to ask.
Also, you can donate your points in dollar amounts to charities. If the Bing rewards program was as malicious as you suggest, I highly doubt they'd let you donate the points to charity.
I'm not sure if I could work at a company that would practice such malicious business practices as well. I have some moral standing and I expect my employer to as well.
I would hardly call it malicious. It doesn't directly harm someone, and most libertarian economists would make the case that you forfeit the information when you make a transaction, but I would definitely say its underhanded and duplicitous and there should be some kind of acknowledgement from Microsoft that they are exploiting said information.
I don't know why companies keep hiding stuff like this. Maybe 20 years ago their business would suffer if they acknowledged they were selling peoples' information, but now that people give it away all over the internet and have no idea how damaging their behavior is, companies like MS and Google could probably knock on residential doors and ask people if they want to try out a new camera that is on 24/7 and streams their lives to talent agencies, and no one would bat an eye.