Sigh...this has been covered OVER and OVER.
iLife has never been a part of the OS. It comes on new Macs, yes, but it is not part of the OS any more than Microsoft Word is part of Windows Vista. They're two separate products that you get included when you buy a Mac. This has always been true, and if you feel that all you got with Leopard was Mail 3.0 then I pity you.