Apple said they want "every Leopard user" upgrade to SL, which means early Intel Macs that shipped with Tiger and were later upgraded to Leopard will also have to be eligible for the cheaper upgrade. So if it checks something, it will ask the Leopard install DVD.
If they wanted "every Leopard user" to upgrade to SL, they would release it for PPC.
Finder's version number has always been 0.0.1 ahead of the OS version number.
Sort of; it's been ahead by various amounts since System version 2.0, when it jumped to 4.1. It spent most of the mid-80s several versions ahead, and then the System version started to catch up; it was 0.1 ahead for all of System 6, for example. (Though the Multifinder, which was still optional back then, had the same version as the System Software -- confused yet?) I don't think they standardized on 0.0.1 ahead until OS X (though maybe they did earlier; I never ran Mac OS 9, and I'm too lazy to boot up my PowerBook 3400 to check on 8.6).