Rangers average height is 73.5 inches (didn't include goalies or Sauer, but included Fierrero and Kreider and Gilroy, etc)
Average weight 206.62
Bruins average height is 73.4, average weight 203.05
Actual size and weight doesn't have much to do with it, the Bruins just have a few fairly large players up front (Horton and Lucic, and Thornton I guess but he's not really a factor that gets a lot of minutes) and some big guys on defense (Chara and McQuaid mainly. Hamilton is tall but still skinny)
Other than that they're pretty average in size. They benefit more from players like Lucic being aggressive...and Marchand being aggressive, etc. It's more a style or frame of mind than actual size problems
Rangers have guys like Nash, Pyatt, Kreider when he's healthy, and Boyle up front. They aren't real tall on defense but in general are solid in size back there