I remember the day the Trackpad update was released that it did include the early 2008 MacBook Pros. I saw the list on Apple's site. Stupid greedy apple probably dropped support for the 2.5 year old $2000 computers so we can spend another $2000 to get a new MBP
Well I actually came here with the same question you originally had and after reading AnonMac50's (I think) comment saying that he reinstalled it and checked some file, I figured I'd reinstall it and see what happens. Despite Apple's list of applicable MBP's, mine does work (and so does yours). So at least we got what we wanted.