Utimately I think you're right. Events like the release of a much more friendlier and/or powerful set of APIs certainly leaves customers stranded, but its much more friendly for developers to say, "here's the older version for the older operating system, but its NOT supported", than "I'm sorry, you can only use our software if you have the most current operating system". It's just alarming to me to not give customers options.
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I don't mind that 68k died in favor of PowerPC, or that PowerPC is dying in favor of Intel. I don't mind that MacOS 9 is dead, and that OS X has a clear and healthy evolutionary path. The Mac OS evolution has lots of corpses. No problem here. I have basic old software that won't work on my latest machine, and basic new software that would never work on my old machines. Big deal That's life. I can still run Windows notepad on Windows 95 and on Windows XP though. Sometimes the details make the bigger leaps less painful.
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Moot point however. I made my $129 purchase. I spent all weekend installing the OS due to strange upgrade problems, and now I've got the latest OS for the next three months. Woo-hoo. If Leopard wasn't delayed, we probably wouldn't be having the conversation anyway.