A 10 doesn't have to mean something is perfect. In-fact, unless the numbers on your scale are intended more as labels than to represent a linear/curved numerical scale (which is a perfectly valid system, but clearly not the one Aldro is using), i think it's pretty illogical to define a 10 that way. There is likely no such thing as a perfect game, thus 10 would become undefinable. Without being able to define both ends of your scale, everything in-between becomes meaningless. You'd basically be saying "I give this game [x] out of perfect", or "this game is [x]% perfect". It doesn't make much sense when you have no idea what perfect means. You might as well give something 6 out of apple, or 9 out of paper bag.
I wouldn't personally give UC4 a 10 (As of chapter 15 i'd give it a 9.0, but if it maintains its current quality through to the end, and wraps up the story nicely, i could see myself giving it a 9.5), but a 10 is what Aldro thinks it deserves, then that's what Aldro should give it.
If Aldro had said "yes, this game is perfect. It has no flaws whatsoever", I would have had zero issue with 10/10s everywhere. It's Aldro's opinion. I'm just scratching my head that Aldro acknowledges the game is not perfect but saw no reason to deduct any points.
Did you actually read my comment? Because it can act as a reply to this one too :p It literally starts with "A 10 doesn't have to mean something is perfect.", and an explanation as to why.