If your workload and department size were increasing, and you still couldn't get the expenditure past your beancounters, then your own company's fiscal policy fucked you, not Adobe.
You aren't forced to upgrade in any way other than your own convenience.
I could keep telling you it's a business reality that you sometimes have to spend money for software, but you want to seem to carry this torch of indignation, so have at it.
Apparently, you work for Adobe, and given the prices they charge, I now understand why you think an extra $2000 is chump change.
I can understand a company not providing support for a retired product (even though less than 4 years seems like an awfully short product life for business software). But to make your files completely incompatible with previous versions, forcing people to upgrade if they want to add one more copy of the software, is really despicable.
Even Microsoft lets you open Office 2007 .docx files with Office 2003 if you install their converter patch. You can also save files compatible with older software versions.
Adobe doesn't have any option like this. If you save a file in CS4, you're just plain fvcked if you want to open it in CS2. A quick Google search would show that my company isn't the only one with this problem.