Info in the Ether
Since upgrading from a dial-up connection to a broadband connection, I abandoned the practice of keeping copies of software freely available on the Internet. This includes applications like web browsers, e-mail clients, and similar tools. My reasoning was that it's easier to download the most current copy of an application if I need it in the future because a new version will probably be released by that time, storing the program can be expensive and tedious (where do I put it?), and high-speed connections can download a 10 megabyte file in a couple of minutes. So, why keep local copies of such tools? Let it exist in the ether like any other piece of the Internet infrastructure.
Unfortunately, software applications are not immune to motives of business-minded individuals. I recently needed to download the XCode IDE for Mac OS X in order to conduct Java development on my Mac at work. The Mac uses OS X version 10.3, which is not the most current release of the OS (10.4). The most current version of XCode (2.4) works only on 10.4 systems, which mine is not. I expected to find a link to the 1.5 release of XCode for 10.3 systems, but found none. Fortunately, I remembered having stored the 1.5 release of XCode on a CD in April 2005, and had the CD conveniently located in a CD wallet in my briefcase. So, I used my backup copy of XCode and was in business. But had I not kept a local copy of XCode 1.5, I would have been screwed.
So, why might Apple choose to not make XCode development tools available for older versions of it's operating system? My suspicion is that Apple is forcing developers to build products for the most current version of it's OS, and carries this out by pulling development tools for older OS releases out of circulation. If this is their goal, then I believe they have been successful so far.
Relying on the ether to be storage medium for infrequently-used files such as application installers makes a person vulnerable to the software vendor's release and support schedule. Since disk space is cheap and broadband connections are nearly ubiquitous, it's like having an enormous storage pantry with a convenience store located next-door. Do you stockpile food in the pantry, or run to the convenience store anytime you need an item? These choices represent a double-edged sword that is tricky to handle.