How will they know who has Leopard and who doesn't? Do they have tabs on that through the serial numbers of the laptops or what?
I assume you can buy the Upgrade disc for $30 regardless of what operating system you have. But, the disc will not work on a computer that doesn't have 10.5 on it.
For example, when the put the disc on a MacBook running 10.4 (Tiger), it will say "Cannot install on harddrive, 10.5 required" or something.
So basically, you can buy the disc but the disc runs a code at startup to see what operating system is installed. So I don't think its relevant if they keep tabs on who has Leopard or not.