game-editor.com

I'm not at all familiar with the GE source code, so I do not know for certain if this is how it works. I am under the assumption that when someone exports a game, no matter what it is, that the entire GE source code compiles, along with the user-created code. Am I correct in assuming that this would cause GE made games to lag more on slower systems? If so, would it be possible to program GE to only compile the parts of the code that are necessary for the game the user is creating? I think this would be a feature that would make GE more efficient.

There isnt any compilation at all. GE is a interpreter. Means, the game-editor writes a datafile and this datafile is interpreted by various engines, for ipad, iphone, windows, and so on.
You might not have noticed that because you got a single windows executable as result. The first part is the engine, the second part contains the code to interpret.