How does that make him a hypocrite? Just because someone wants the PC maintained as an open platform doesn't mean that they're opposed to closed platforms. There's plenty of room in the market for open and closed systems. Some people will demand open systems because it offers them more freedoms. In Notch's case, that was probably the freedom to develop his own software. Other people will prefer closed systems, since it provides an extra layer of protection from malicious software and it provides a degree of quality control. (Well, in theory.)

Now there is a bit of a problem with the WinRT API: they have the potential to close off Windows, which is somewhat open. It isn't an issue at present since the Win32 API is still there. It may never be an issue because Microsoft may be forced to leave Win32 as an open API. (Incidentally, do they still call the API Win32 on 64-bit versions of Windows?)

Another issue may have been over UEFI and signed kernels. I kinda suspect that this is what Notch is actually referring to since "nobody owns the PC" doesn't make much sense in the context of Windows. (Microsoft owns Windows. Even if they leave the system open for developers and consumers, they still control the future of Windows itself.) This has the potential to make Microsofts, and a tiny number of other vendors, owners of the PC. But that will only happen if hardware vendors start turning on signed kernels.