RamonS wrote:XP is still supported by Microsoft and that should be the general rule as to which OS an app should support
My point is not, whether MS is supporting something, but what you developed the software for.
So more precise examples for all the smart asses on this forum

:
If you need .NET Framework 4 for the software and a customer doesn't want to update to that framework, but wants to run the software on .NET Framework 3 ...
If you develop it for 64-bit OS and the customer wants to run it under 32-bit ...
And:
The requirement to download and install a FREE software is a lot less restricting than updating the OS, because
- you will have to buy the OS,
- maybe buy more new software because your usual software packages don't run with the new OS anymore and
- you have to install it on probably quite a few computers in your office to keep things working
And on top of that:
- you might have to buy new hardware, because your old hardware might be to small/slow for all those new software packages