Todd,
Yes, I ran into this too. And I suspect that everyone does who takes the time to measure the deflection limits (kudos!).
Possible interference of the linkage with the elevator skin is not the problem (also common, but it's a separate issue). With no interference, the travel is still limited to about 40 deg total as you said. It's simply that the maximum travel of the Ray Allen servo, coupled with the lever arm length of the trim tab horn, just doesn't give quite the specified amount of trim tab deflection.
I spoke with Van's about this (a few years ago). They indicated that this is normal, and that the available travel should be sufficient under all flight conditions (which begs the question: why did they specify wider travel limits in the manual?). Anyway, I'm not flying yet, so can't confirm first hand, but that's what I was told by Van's.
-Roee