Fine by me. I expect my Core 2 Duo MacBook (late 2006) to lose support one day, probably the next major OS revision.
It's not like I'd expect a five-year-old Wintel PC to run Windows 8 when that's released.
Apple (and other OS developers) need to balance innovation with supporting older architecture and hardware platforms. By not supporting older architecture, they gain more freedom in pursuing functionality that requires the more robust capabilities of more modern hardware.
Of course, Apple makes its gross margins selling hardware, but let's not forget that they are basically a software-focused company that creates functional ecosystems that run best on their proprietary hardware.
You don't buy a Mac because it has a certain Intel CPU; you don't buy an iPhone because it has a certain ARM processor. You buy it for its ability to run a bunch of great applications and services that (more or less) co-exist peacefully on the same system, whether it be OS X or iOS. That's what an operating system is: a big complicated program that lets other big complicated programs live together in relative peace.