Rich,
From experience, after the release of Leopard (last year) all new machines come with the OS. At the retail stores, there's a supplement Install DVD in the box.
Apple's policy on exchanging products has always been 14 days of a launch date.
For example, if you bought Tiger within 14 days of the Leopard release, you can exchange Tiger for Leopard with no additional cost. Be careful though! This is for APPLE ONLY! Their resellers have different rules.