Jeremy,
I'm at a loss. The only difference I noticed is that the map service you are using has your layer ID 2 as part of a group layer. Admittedly this is a very thin hypothesis, but maybe there is a quirky sort of bug related to group layers and definition expressions?
Ben's example is not directly using a layer within a group layer, but his service contains group layers. Robert's example is using a service that has no group layers present. My example also has no group layers present. I'm not sure if there is any merit to the idea, and I don't have the time available to exhaustively test this, but maybe you do have the time?
As an exercise, I copy/pasted your code block into the v2.4 viewer I am upgrading to. I did change the value from 'BIA' to 'FS' because I know that we have U.S. Forest Service lands in reasonable proximity to our city. I kept zooming out and noted that there are other labels (part of the map service group layer) that indicate features that the definition expression is eliminating, so your code appears to be working correctly for me. See the attached screen shot. There goes the group layer bug theory! [maybe]
It probably goes without saying, but you are using this tag against API 2.4 and not an earlier version, correct? Just trying to cover the possibilities...
