But iPads and Android tablets don't have a UI that practically requires the precision of a trackpad. Obviously you don't have to use the Desktop on your Surface 3, but Microsoft is clearly pushing that as a core feature.
I can't speak for the Surface 3, but I have owned a Surface Pro 3 for a good while now. I _never_ use the trackpad. Browsing, office, even doing software development can all easily be done using finger and pen (for when you need finer control). I've gone so far as to check if there is a Type Cover for it that doesn't have the trackpad, but uses the space for something else.
I know it's the popular thing to say that Windows 8 isn't fit for touch devices, but it's outdated and usually only reiterated by people who don't have any proper experience doing it.
You can use a $5 mouse or keyboard from any manufacturer with it. It's got USB and Bluetooth. Nothing about the UI requires the undersized "trackpad" built-in to the keyboard covers.