Although look amazing There is still a considerable number of users who use Leopard as their main operating system on a daily basis, something that Apple does not like too much if MobileMe is also used because they will deactivate this service in a relatively short time.
What Apple is doing with users who use MobileMe in Leopard is to offer them a free copy of Snow Leopard so that later if they want (and can) buy Lion through the Mac App Store, something that cannot be done from OS X 10.5. It is a decision at least curious and that I remember without recent precedents.
If you meet the conditions and want to opt for your copy of Snow Leopard you must visit this link.
Source | 9to5Mac