That IS a joke, right? If not, which operating system will it have? Windows 7 with its bloatware effect and lack of touch compatibility? or that 'hugely successful' mobile OS?
You do realise that the OS is the key to tablet success? iOS was designed for iPad initially. Market forces persuaded Apple to release the iPhone first. So what we have is a mobile phone with a tablet OS.
Microsoft have been locked into the idea that the 'Slate' has to be a fully functioning PC, when all the evidence is that it does not.
So now Ms are in the curious situation where they have an embarrassment of operating systems [in more ways than one], ie: two, but neither was designed for a tablet or slate.
As Grady Seasons said [to Tom Cruise's Vincent] It's like a nightmare, isn't it? It just keeps getting worse and worse.
I think he was just being sarcastic. So yes, he was joking.