which means either the BSG cast are strangely small or Everybody on Firefly is freakishly tall.

Adam Baldwin - 6'4"
Gina Torres - 5'10"
Nathan Fillion - 6'1.5"
Alan Tudyk - 6'
Jewel Staite - 5'5.5"
Morena Baccin - 5'7.5"
Sean Maher - 5'10"
Summer Glau - 5'6.5"

Average Male Height - 6.07 feet
Average Female Height - 5.61 feet

Edward James Olmos - 5'10"
Jamie Bamber - 5'9"
James Callis - 5'8"
Grace Park - 5'9"
Tricia Helfer - 5'10"
Katee Sackhoff - 5'6"
Michael Hogan - 6'
Mary McDonnell - 5'8"

Average Male Height - 5.81 feet
Average Female Height - 5.69 feet

So yes, the male cast of Firefly on average significantly taller.  The main women on Galactica beat out the women of Firefly.

Just for comparison, the average North American (and pretty close to the same for the UK) is 5'8.5" for males, 5'3.5" for females.