I find that pretty silly, and I don't see a real reason why they didn't just make the machine dual-boot both Windows and Android. If users want Android apps inside Windows, they can download Bluestacks themselves. So the only explanation is that Microsoft is coercing manufacturers into not allowing Android or other OS's alongside Windows.
If they are doing this now, and more Linux vendors start asking for Microsoft's "permission" to boot their OS on the Windows machines with UEFI, what's to stop Microsoft from denying a UEFI license to someone who's starting to become a "real" competitor to Windows (like Android is, in some cases)? What if Ubuntu gets to 10% market share in the next 5 years, and keeps growing? Will they keep giving Canonical the UEFI license? What's guaranteeing that they will, if they are already banning Android from the Windows RT machines?