Daiku brings up good points.

I just find it easier to saw from behind when I can instead of over the saw.

What is the depth of cut at 90 for the thirteen inch saw? The reason I ask is that the 10" saws can cut just shy of 4". Good for almost all shoulder cuts and drop cutting tenons 4" tenons.
The only time I could see the thirteen being needed is for tenons longer than 4". Maybe the depth of the thirteen can pass through nominal 6X (don't know). It just seems that the sixteen would be a better purchase for saving money.

What are the advantages of the 13 (besides being lighter)?