For what it's worth, here's something that might help address some questions about the Snow Leopard install process. I don't know if the "Apple Experts" on the store's chat support know anything, but here's what they had to say...
Apple: Hi, my name is [redacted]. Welcome to Apple! Good evening. How may I help you today?
Me: Hi, I have a question about Snow Leopard.
Apple: I'm happy to assist with that.
Me: I have a MacBook that I haven't used in a few months, due to a hard drive failure. The machine is, unfortunately, no longer under AppleCare.
Apple: I am sorry to hear that!
Me: It was pretty upsetting, but hey... I know I need to backup from now on!
Apple: I definitely agree, backing up is very important!
Me: There isn't an Apple retail store anywhere near where I live, however there are a couple Apple authorized service providers.
Apple: What can I do to assist?
Me: Well... They can fix my MacBook by replacing the drive (for a cost, obviously). However, they won't install Leopard on it -- just the cost for a replacement drive and the labor charge.
Apple: Ok sure.
Me: So I was wondering, can I buy Snow Leopard and install it on the drive? Or do I need to do something else. The people at this place in town said Snow Leopard was "upgrade only" or something like that. But I had Leopard on my MacBook before it crashed...
Apple: You should be able to install Leopard first with the discs that came with your computer. Once you do that you can then install Snow Leopard with the upgrade.
Me: I see, I see. Okay, that shouldn't be too difficult! I just have to find the box now...
Apple: May I help with any other product or order questions before you proceed?
Me: Nope, thanks for the help!
Apple: You're welcome. Thank you for visiting the Apple Store. We appreciate your business. If you would like more help, please chat with us again.
(Note that I made this whole situation up, as I tried this several times and Apple shot me down with their BS statements.) The bolded statement indicates that for a clean install of the OS, you will have to either first install Leopard or get the Mac Box Set.