I agree. If the Trek feels better, get that.

That said, I'd be surprised if it actually is much lighter. Probably the fenders make the biggest difference. The Trek has similar components to the Jamis Commuter 2, except for only having a single chainring (which I think is an advantage for the Jamis unless you have really steep hills on your route). Stiill, the geometry of the bikes is different enough that I'd definitely choose based on feel.

If you can find a 2012 Trek FX 7.2, you can probably get a deal on it. MSRP on the 2013 is $550, so your dealer can probably come down a bit.

The biggest difference between the two Jamis bikes is the internally geared hub on the 3. That's nice for keeping maintenance low, but it also adds a good bit of weight.