With Nintendo struggling to juggle Wii games on the Wii U and Sony's Playstation 4 abandoning current gen PSN games, it looks like backwards compatibility is a thing of the past.
You had the mass market ones, like eHarmony, of course, but there were those that tried to find compatibility based on religion (like JDate), or even your profession (Farmers Only).
Windows 8 and Atom devices also provide compatibility with millions of hardware peripherals like printers, mice, keyboards, cameras, receipt printers, fingerprint readers, etc.