My TL;DR contribution:
Warriors (generally) have a higher BLOCK VALUE, but low BLOCK RATING. This means they don't block as often, but when they do they are more effective than paladins.
Paladins (generally) have a higher BLOCK RATING, but lower BLOCK VALUE. This means they block more hits than a warrior, but each hit blocked isn't as effective as a warrior's block.
In theory, the overall net effect is about the same until you start getting into some very specifc situations.
All Block (either rating or value, although the OP was referring to rating) has been dropped from T9, presumably until Blizzard has finished its quiet contemplation and implemented its promised fix to the block system as a whole.