Interesting post from 2005 on the US/UK pack difference.
“We actually made different versions for the two countries. Neither game style is better – the English one is only set up to have two players, but because it’s on a map, they have limited space and are basically forced into fighting each other more. The game is slightly more complicated because of the increased number of dice. The American version is great because you can have tons of players, it’s not as complicated, and the game can be played for a long length of time because the space is not limited.
WizKids, Inc.
Beth Kirschbaum
Customer Service
Front Desk & Supported Conventions Coordinator”