It will be interesting to see what happens the next time Apple needs to drastically overhaul their language and how gracefully it gets handled. I think they did a decent job in handling "classic" applications.

Why can't Microsoft do the same thing? Abstract out support for old versions and build something concrete that can be expanded. OSX has been around since 2001 with steady improvements with each upgraded version. A lot has changed on the outside as well as under the hood but the same core architecture is still in place. Why? Because it works very well, is modular, and can be improved without a massive overhaul.