well you could be right. However i based the starting point on the fact that todd was moving down mountains (as seen by the decay of snow as he progressed) as well as the crossroads he crosses (when the fox hunts the rabbit). It may be a little less but he is definitely descending down that mountain chain.
Makes sense, though the accuracy of the map is questionable of course. As others have pointed out, in the demo the road follows the river for awhile. Going by time alone, it takes him 2 min., 23 sec. to get from the start of the demo to the standing stones, compared to 2 min., 36 sec. to get from the stones to Riverwood (minus the one lengthy time he spends showing us the menu features). So, the distance between the X on the map and Riverwood should be fairly close to equal the distance between the start point in the demo and the X.
The demo appears to end a bit south of Whiterun, not far from where he exits Bleak Falls Barrow. All total, I'd put the length of his path at about half what you've got.
Of course, we may both be wrong. Guess we'll find out the truth in 27 days. :foodndrink: