Starbucks: That additional foot traffic is around 1/20th of what they get from an iOS or Android promotion. Advertising the promotion to get that foot traffic costs more than revenue generated
Microsoft: Would rather spend the funds to create new consumers instead of giving existing ones free stuff
Advertsising the promotion? It would take printing an extra code and the WP logo onto the already existing cards. Again, that is if Starbucks is the one eating all the costs here. Everyone keeps repeating this, but I am not so sure. Do we know that Apple has "nothing to do"* with the free apps Starbucks offers?
Also, while I get that MS would rather spend the money getting new consumers, EVERYONE is enveloped by apps, apps apps. What is the first question people ask about any OS when switching? "Can I have my apps back?" Giving away said apps would all be part of it.
Another thought I had, though costs would be even higher per person, is if there was some way to prove which apps you purchased on another platform and then having MS "transfer" those apps to your phone for free. That would do a lot in getting new users to adopt the platform. My wife is excited about WP too, and will be getting one with her concession line here soon, but her biggest gripe is having to deal with rebuying a lot of apps. Granted, for her, it's going to come out to < $10, I am sure, but still. People don't like to repurchase something they have already bought, even if it does turn out to be only a couple of bucks.
*By "nothing to do" I mean that Apple isn't helping pay for or subsidizing the apps in any way.