I just watched his BB.com video w/ cutler and he talked about his arm size. Even the pros exaggerate, he's just honest. Just watched another video of some new pro bragging about his 23" arms and someone busted out a tape measure and they were 21.5". I forgot the kids name, but you can find it on youtube.
And, each additional inch is a huge increase in arm volume. Exponentially huge.
Circumference = 2*PI*Radius
Volume = (4/3)*PI*(Radius)^3
So, the volume/circumference ratio is (2/3)*(Radius)^2
And, since Radius=Circumference/(2*PI)
The ratio can be seen as:
(2/3)*[Circumference/(2*PI)]^2, i other words, the bigger the circumference becomes the volume must grow by a power of 2 MORE ( volume is a power of 3) just to catch up, that's huge size and exactly why an inch seems like such a huge difference, because it is!