Let's look at the size of those "power" defensive teams you are envying.
1. Pittsburgh
DE Aaron Smith - 6'5", 298#
DT Casey Hampton - 6'1", 325#
DE Brett Keisel - 6'5", 285#
OLB Lamarr Woodley - 6'2", 265#
ILB James Farrior - 6'2", 243#
ILB Lawrence Timmons - 6'1", 234#
OLB James Harrison - 6'0", 242#
S Troy Polamalu - 5'10", 207#
S Ryan Clark - 5'11", 205#
CB Ike Taylor - 6'2", 195#
CB William Gay - 5'10", 190#
2. Tennessee
DE Jevon Kearse - 6'4" 265#
DT Jason Jones - 6'5", 280#
DT Tony Brown - 6'3", 290#
DE Kyle Vanden Bosch - 6'4", 278#
WLB David Thornton - 6'2", 225#
MLB Stephen Tulloch - 5'11", 235#
SLB Keith Bullock - 6'3", 235#
S Michael Griffin - 6'0", 202#
S Chris Hope - 6'0", 208#
CB Cortland Finnegan - 5'10" 182#
CB Nick Harper - 5'10", 188#
Wow, those teams are so much bigger than the Pats. No wonder they're so much more physical. We only have 330# Ron Brace, 325# Vince Wilfork, 310# Myron Pryor, 300# Ty Warren, 300# Mike Wright, 285# Jarvis Green, 270# Adalius Thomas, 260# Derrick Burgess, 245# Jerod Mayo, 245# Gary Guyton, 210# James Sanders, 210# Patrick Chung, 200# Brandon Meriweather, 204# (6') Shawn Springs, 193# (6'1") Leigh Bodden, among others. We obviously are a Colts-style finesse defense who can't physically stand up to the big boys.