Not sure where you are getting your specs, but right off of the BMW Motorrad USA site:
The weight difference fueled and ready to ride is 53 lbs....that is substantial. I am not argueing whether it is easier or harder to ride...that is this discussion and there is alot of support for the 12 even off road. I am merely talking about pure riding weight. Then the difference in the GSA, mostly fuel and crash bars, is ANOTHER 39 lbs for a total of 92 lbs more than a 800.
I do agree that with bags and the jugs sticking out and acting like a kick stand of sorts, the 11/12 bikes are possibly easier to pick up, on DRY ground. In mud the jugs make act like anchors burying into the mud...both bikes have pros and cons.
For the average BMW rider, I would say the 12 is a bit more practical bike that the 800, but that does not discount the fun factor of a more dirt bike feeling GS that you get with the 800.
ps: Yes the 800 has a longer wheelbase, but the longer Overall length is a combo of the extra wheelbase combined with a 21" front wheel over the 19" on the 1200. That may add length, but that also adds off road capabilities...I know there has been discussions on that here, but a 21" is better in most off road situations. +1 point for the 800 off road. Easier ? Insert Personal opinion here...