I think the fact that it's been loaded with upgrades (Thunderbuckers, custom bridge, hipshot tuners, etc) make it distinct from your usual Bird listing. I don't think it's really rare in a collector's sense, but for someone that's looking for a specific list of upgrades, it definitely makes it unique.
Of course, you could just modify most any modern Bird to match this one, but it would probably cost a lot more. Besides, it came with all the stock components should I ever want to switch things out, but the upgrades made the bass more appealing, at least to me.