(Dropped w95 thought. )
The reason is, simply, that I don't yet have to.
For the most part, the rule for making a program compatible with down-level operating systems is as follows: don't use functionality that isn't available. I claim that this isn't that hard. If all you need is to call GetLongPathName(), simply check for the entry point using GetProcAddress(), and if it isn't present, emulate or stub it. It's poor style to fail to load on Windows 98 just because you called GetModuleAddressEx() in one spot. Using Unicode entry points can be a problem, since very few functions have their Unicode versions supported on Windows 95/98/ME, but UNICOWS, the Microsoft's Unicode API emulation layer, is available for that if you want to take the easy route.
Now, there are a couple of good justifications for dropping Windows 95/98/ME support. One is memory: if you require at least 1GB of memory, you might as well drop 9x support, because there are very few stable 9x systems out there with that much RAM due to a kernel address space problem with the default cache behavior. The second is testing -- the share of 9x systems out there is minimal at this point, and in commercial development, it probably isn't worth the cost of testing those platforms. If you don't test those platforms, you might as well not support them at all, because you won't be able to state with confidence that it will run on 9x platforms or devote real development time to fix any problems that are found anyway. On an open-source project with less formal development/release/testing processes, however, there are fewer excuses.
In VirtualDub's case, there are also more specific circumstances in which it would be very annoying not to be able to run on 9x platforms. Some video capture devices never made the transition successfully to the NT driver model, and thus are permanently stranded. Other devices performed better under 9x, at least at one time. Finally, there are some perfectly good 9x systems out there that can't make the jump to XP, either due to general lack of drivers, or due to memory; VirtualDub and Windows 98 will run comfortably in 96MB of memory, but you would have to be insane to run Windows XP on that much. I see being able to run on these down-level platforms as a distinctive feature.
This post has been edited by Fredledingue: 22 May 2008 - 02:16 PM