I'm kind of surprised the Trek was lighter. I bought my Sirrus last year specifically because it was the lightest weight bike in my price range... although it's a Sirrus Sport (which is a lower model than your Expert) and I was testing it against lower model Treks (7.2 FX and 7.3 FX), plus they were 2009s, so I realize it's not that relevant to your situation...

At any rate, if I were you, I would go back and test ride the Trek again, maybe even a few times, and compare it with your Specialized. Bring the Specialized along with you to the Trek place and ride them one right after the other, back and forth a couple times. That's really the only way you'll be able to make a good comparison because you'll forget the subtleties of each if it's not back-to-back.