It even varies from printing to printing. Unlike your Knightfall trades, one of mine has DC logo of a different size (just like your NML trades). My NML are actually on the way, and I guess they will differ in similar way. I learned very quickly not to care about that, what with the Marvel logo change, different shades of the colours on the spines in one book series... Sometimes the books are not even the same height.
EDIT: It's actually neat how Cataclysm almost matches NML considering they came 3-4 years apart. Hopefully the upcoming Road to NML (and potential Aftershock collection) won't ruin it as they are supposed to come between those books.