The problem with Apple not supporting OS X versions in major circulation is all the "new to computer" using types that perhaps at best run Software Update and EXPECT Apple to be taking care of them and have no capability to upgrade the OS and the risks involved in that action.
Nearly 90% of all computer users, and nearly all coming from Windows, expect the operating system to work as long as the hardware does, with only minor patches etc.
They don't expect Apple to suddenly drop them for necessary security patches.
If third party software like Java doesn't issue a 10.5 update, then Apple should disable it and notify the user it's no longer supported.
The real reason is because Apple doesn't support older OS X versions and thus third party software, who needs the cooperation of Apple to fix THEIR issues in OS X, don't bother.
So it's Apple to blame.
Microsoft supports their OS versions for 10 years, Vista, 5 years old, just got another 5 years of security and stability support.
With most Mac's only being able to handle 1 or 2 OS X upgrades at best, and Apple releasing a new OS version every year now, means a new Mac is going to be obsolete after 2 years, even though the hardware can last considerably longer.
It's wrong of Apple to think of all their users as competent or knowledgeable to upgrade their OS (and brick their third party software and hardware drivers) when they are not.
People are drawn to the Mac because it's supposed to "just work" and it only does so for a short time.