Vista and older software

[#1]

My friend is a family history fan and she started her research back in the days of Windows 98. She used some software called Ultimate Family Tree. Unfortunately, it didn't work on XP, giving a Divide by Zero error (I understand that this is to do with the speed of the computer).
After a lot of fiddling about which consisted of downloading a patch and using command prompt, I managed to get it to work.
Now that she has Vista we were resigned to the fact that it wouldn't work with or without said patch.
How wrong we were - she put the original disk into the laptop and it worked perfectly.
Can't understand why such an old piece of software should work out of the packet but with all the complaints about Vista not working with this or that, I was both amused and bemused!  Can anyone hazard a guess as to why this has happened?

[#2]

They did with vista create a database which is updated a lot that contains details of how to run old programs. You dont see it but it can run old software based on this database. May be your lucky that someone has added this old software to the database.
There isnt really any reason why old software wont run unless it makes low level calls like a scanner, if its just simple software it shouldn't really be a problem. Some software may check what O/S you are trying to run it on and may bottle out if it finds something new as it wouldnt know about win2k or xp

[#3]

Very true.
I recently had a customer who was concerned about an old Lotus spreadsheet that had complex macros that couldn't be rewritten for more recent versions of that or Excel. It was running on a "fading" win 98 system.
But I tested the old software (over 10 years old by now) and it installed happily on both XP and Vista and the spreadsheet and macros worked fine.

[#4]

Thank you for the replies. It makes a pleasant change to hear of something that will run on Vista after all the grumbles.
I've still got some old software so I might go and have a play.