Okay, maybe "rarity" wasn't the best reason for it.
If they think it's worth releasing like this, if it makes more sense to everyone, and people think it's worth buying, then sure, why not?
I just personally wouldn't, that's all. Like when they released Desperado with Once Upon A Time In Mexico. It's like, hello, what about El Mariachi? You wouldn't see them releasing a Star Wars box set and not including, say, The Empire Strikes Back, now would you?
But ignore me. I'm just the picky guy who always thinks it should be all or nothing. I'm the guy who hates it when they don't have everything they could put on a DVD, and then complains when they put something else not directly related to the film on that film's DVD.