Sometimes OSes are deemed obsolete for whatever reason, and browsers -- all of them! -- simply stop developing for those OSes. This means that you're at least shelling out the cost for a new OS, which can be (1) painful (if you're using Windows or Linux in some cases) or (2) impossible (e.g. if you're using Mac OS X and Apple has decided that your hardware is "end-of-lifed" -- e.g. PowerBook G4). If you're one of the unlucky ones to be in the latter category, you actually have to shell out enough money for at least some upgraded hardware (perhaps in addition to the OS), or possibly a brand new (or newer but still used) computer, which will likely be a lot more painful than just shelling out for the OS.

The key point is that Google Apps are tied to browser versions, and browser versions are tied to OS versions, and OS versions aren't exactly consistent in their support or end-user coverage. Users who figured their current setup works well enough for now, and who for many years haven't had any reason to upgrade will now be forced to if they want to make use of those Google Apps -- or, they can take the much less costly route and simply not use Google Apps, or deal with "simple HTML mode" or whatever.

The worst part about this that irritates me most, though, is that many of these systems simply don't have anything wrong with them except that someone, somewhere, arbitrarily decided they were "too old". So perfectly functional pieces of equipment now lack functionality because enough people have arbitrarily decided that they "don't have" that functionality anymore, even where it might actually be possible.

On the plus side, it does mean that no one has to support old browsers' quirky and always-varied interpretations of the same chunk of code...

It is if you're in a large organization, or you want to make sure thngs don't break before you release them to your users.