You can't make a modern OS and still be compatible with 20 year old programs...
You can still run DOS programs on Windows XP (never tried that on Vista) I use Tango to open some old schematics we still produce today. They have more than 20 years difference, and are compatible.
I think the good part of the Amiga spirit that I really miss is inovation. It would be awesome to have a compatible today, but that would be really useful just for fans like us.
There is a place for something really innovative like the Amiga was at the 80's. Take a look at the PC's hardware. They are all the same crap, including Macs. All the "modern" OSs are mammoths, eating tons of disk space, RAM and processor power.
I would like to have all of these resources available to my software. I really believe there are many people in the world that are tired of waiting several minutes to boot their computers, tired of pressing ctrl-alt-del, and tired of waiting for simple things like window movement if the computer is busy.
Hope some company take the "Amiga way" and do something to change that. This is what I believe the Amiga was all about: do everything better, easier, faster and still have a nice price. It is not about being compatible with the past, but be the future today.
...now I will fall from the clowds and keep driving this stupid PC :-(