Customers pay and pirates plunder.
Software pirates will find a way to steal things they are unwilling to pay for. The smart companies in software will work to serve their customers and leverage the pirates for their one valuable quality - free marketing and distribution.
Another way to look at it is the reason the F2P + micro transactions works is the same reason that shareware works, lower the friction to enjoy the product and make it easy to share. Sharing is valuable.
Video game companies are so much hoping to stop piracy or used game sales that they forget that sharing a game with friends is free advertising and marketing for them.
If League of Legends wasn't free, I probably wouldn't have tried it, but because it is free to play a lot of my friends have played, purchased, and enjoyed the service. Apparently Team Fortress 2 makes 3x more money as F2P than a traditional $50 boxed game.
To me it boils down to getting your product into the hands of people who are willing to pay for it. If people aren't willing to pay for it without DRM, adding DRM won't make you more money, it will just piss off the people who were willing to pay you in the first place.
I'm kind of surprised how many of my hardcore gamer friends are anti Xbox One already simply because of the way MSFT is going to handle used games and DRM. They're losing the hearts and minds of their core market.