The iPad and its ilk acknowledge the form factor's weaknesses while playing to its strengths: it's portable and tangible for looking at content. Thinner, lighter, longer battery life are consistent with these strengths. Microsoft is going in the opposite direction with Surface Pro: thicker, heavier, and shorter battery life. This direction slightly helps tasks which are a weakness of the form factor (content creation), while undermining tasks which play to the strengths of the form factor.

I apologize for not being clear. It is my understanding that the Surface Pro is marketed as a tablet that is also a laptop replacement. I am arguing that current tablets cannot satisfactorily replicate the functionality of laptops.

The iPad, Nexus, etc. are marketed as supplemental devices, not laptop replacements.

I'm fairly certain it's because the Surface has the keyboard-kickstand thing. Ipad doesn't. A few Asus models do, and perhaps some others I'm not aware of, but given all the advertising of it the Surface is the most notable.