Well, it's a wild guess, but you can consider that IBM would sell less if they contributed less to Linux (as you quoted, «it also provides flexibility, choice, and an attractive total cost of ownership that can benefit IBM customers.», and customers bring money) So it is fair to say that IBM earnings are partially caused by the Linux servers attractiveness, and that they effectively earn money from open source. It's not because you don't sell something that you don't earn money out of it. There are different business models out there.