sigh... I'll humor you... hrm... I'm too lazy to look up the exact speeds, but I believe the saturn ran at around 28 mhz... while the dc ran at around 280... with all this extra speed it's easier for the DC to render more polygons, not to mention that the DC has a better GPU. What your asking is essencially the same as asking "Why can we port Dreamcast games to the NES?"
and the reason why most of us like the saturn/try to keep it alive, its a good console, with some unique games (nights for example), and for the same reason there are numerous sites keeping most of the now defunct and discouninued consoles out there avile so to speak
Bad ports (and the majoirty of DC games would inevitably not be as nice on Saturn) are not the way to keep a system alive; people would likely just prefer the original to a watered-down port. I think what Saturn really needs to keep it going is people who can write interesting programs for it, people who can engineer interesting hardware for it (and hopefully keep the system running) and people who enjoy using the resulting software and hardware.
By the way, Dreamcast is not a Windows platform, except in the sense that it can run a custom version of Windows CE that was not intended to be used for most games.