Cringely thinks it’s simply to stop Google getting it:
“Were Google to buy Skype they’d convert those 663 million Skype subscriptions to Google Voice and Gmail and in a swoop make parts of Yahoo and MSN irrelevant. They’d build a brilliant Skype client right into the DNA of Android, draining telco revenue and maybe killing smaller players like Windows Phone. They’d cut deals with equipment makers like Cisco (Linksys) and NetGear and steal voice revenue from telcos and cable companies alike. That’s all Redmondesque behavior and if anyone is going to be behaving that way, Ballmer feels, it had darned well better be Redmond.”
That sounds like a perfectly Redmondian argument to me.