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If I'm not mistaken, what Jeff is suggesting only works if your project only involves one Revit file. If you're scheduling elements from linked files, as far as I can tell there isn't really any way to identify elements other than duplicating the schedule in each linked file, and then choosing Show from the schedule.
Why ID woudn't be schedulable seems inexplicable, but as of Revit 2013, scheduling remains pretty primitive. Many things one might expect to get out of the box via scheduling (such as filtering on family or type, or sorting or filtering on more than four fields), can only be accomplished through the API or DBLink.
Joel