This could go on forever, but I disagree.
I'll try not to drag it out too long
JDG doesn't drift out of games... because he is seldom in them to begin with. Unless we are absolutely murdering a team I often forget he is even playing... until he stolls up to take another poor corner or free kick like he is the main man. He rarely presents himself for a pass, and when he does get the ball he dithers for an eternity. It is hugely frustrating seeing time and again both the pass that he should make, and the pass you know he will (eventually) make.
Also, he doesn't just shirk 50/50s, he neglects his defensive duties completely. He almost stops when we lose the ball, or makes a token effort to move slowly towards the nearest opponent. He affects nothing, bar our shape and defensive numbers. It wouldn't be so much of an issue if he's playing behind the striker, but he isn't.
Ki on the other hand is always available for a pass, and when he does get the ball he recycles quickly. He might make a lot of short passes - that people dismiss as doing nothing - but if there is a more speculative option available he has no hesitation going for it - and succeeding, due to his ridiculous technique. Incidentally, it is strange how he is derided for this, when it is the very thing that Leon Britton (who I have no particular issue with) is lauded for.
Anyway, the other criticism fans have levelled at Ki is his lack of goals, especially in comparison to JDG. Ki played a lot deeper for us than he did at Celtic and with S. Korea (with whom his scoring record is fine) though, and JDG played predominantly behind Michu last season so was bound to carry more of a goal threat. So, moot point there.
Finally! Defensively, I admit Ki is no Makelele but he is far more influential than JDG. As I said, he isn't naturally a defensive player so shouldn't be castigated any more than JDG for any shortcomings. He will always try though. He maintains discipline and tracks people... which is good enough for me.
End of rant :]