And your software ran on Vista without incident and without having to port it? And I would guess you didn't use the MSI installer, since that was broken at launch.
Adobe CS3, Bit Defender, Zone Alarm, Norton... And those are just off of the top of my head. I believe they have all been updated and work now, although I think SP1 re-broke a few of them. I personally only use CS3, and prefer NOD32 and other tools to Norton's suite, but it remains that a number of popular products broke on launch of Vista.
It could be said that buying the new Vista versions of the software would fix the problem, but again, why pay all of that money just to maintain the same level of performance? I can always find better things to do with my money than throw it down a hole.
And that would be the personal preference part. I have never had a single issue with XP, so Vista is nothing more to me than a very expensive complication I do not need. Too much of my dev software has Vista issues, including some of MS's own tools (although I would assume the MS ones have been fixed by now).
Companies have to spend resources to update their software to Vista, and they have to pass those costs on to the consumer if they wish to stay profitable, or even just to break even. So the consumer is once again spending money for no tangible benefit.
It just seems like very easy math to me, Vista is a money pit. You keep throwing money into it and getting nothing in return.
I really wish Horizons devs didn't have to even bother themselves with Vista, because if none of our players were having issues due to switching to Vista then the devs could spend their valuable resources on other priorities.
Fewer resources being spent on OS compatibility would mean more that might be spent building a custom launcher.