Quote - It's disappointing to see Python going the QuickTime route. I have a handful of purchased products built in Python, and apparently they will not work in a new version of the application they were written for because the new app includes a newer version of Python.

When the products are supplied as PYC files (i.e. compiled Python bytecode) or PYD files (compiled C/C++ etc extensions) instead of just as PY files (plain text), you always not going to be able to use them with older or newer versions of Python due to changes in the core that are binary incompatible (this is expected and is why the version number changes).
Even scripts aren't immune to problems, as modules in the library due change, get deprecated, are removed, or replaced with differently named ones.

Poor version checking in applications like Quicktime is due to a lack of testing.

Problems trying to run old applications on new operating systems often means that they run into problems such as the return values of system calls (e.g. "How much memory is available ?"), return values that don't make sense to the application (P4 required a patch to cope properly with systems that had more than 1GB of memory).
Old installers often have trouble with the huge size of hard disk available today and report negative free space.