krusty did that because he thought it made reading the altimeters in german aircraft easier. you can modify any/all textures in a skin, not just the external ones.
I think it looks kind of silly and the inaccuracy is silly as well but to each their own I guess.
By the way those skins have been in the game, and the same way, since like '06-'07
obviously it's not going to completely accurate because german instruments were in a unit system that makes sense but I think that HTC's gauge has a much better feel of an original