Feature availability may vary by device.
They state this because you OBVIOUSLY won't have touch interface on non-touch devices, and thus any/all touch features available in the OS will not work on that device (that is just a single example of features that will vary, large screen UI won't make sense to use on a 4 inch smart phone, phone capabilities won't work on a desktop with no phone number, picture taking won't work on a device without a camera, etc., etc., etc., the list goes on and on).
Some editions excluded.
This is explained. They exclude upgrading Enterprise editions of the software. Those editions were purchased typically as site licenses for businesses, and are excluded. You need to arrange new site license agreements (or maintain your existing ones) in order to upgrade your windows licenses (in which you will be covered by your site licenses, and not the free upgrade license anyway).