Generally speaking you're only going to be able to fit two source files side-by-side on a ~13 inch laptop screen regardless of the aspect ratio. So the advantage of a 4:3 or 3:2 (which is what Microsoft's Surface line uses) is a little more height and a little less width than 16:9. Usually this means taking away some of the unused gutter space to the right of each source file you have open (less horizontal space) and giving you more visible lines of code (more vertical space).
The bottom line: more visibility of source code.