Only some newer motherboards don't have them, they are becoming obsolete, the new line of legacy free Abit boards do not have PS/2, Serial, Game, Parallel or Floppy connectors anymore.
Aside from the floppy disk connector the rest are useless as people upgrade their hardware, printers and scanners are now all USB, joysticks and gamepads are USB, PCI modems do not use serial ports, keyboard and mouses are all USB, and they will work in DOS or Safe mode since the BIOS will automatically emulate PS/2 mode for them. I actually used a USB mouse in Windows NT 4.0 the other day, it picked it up as a PS/2 device.
These things are just useless now, they hog IRQs and do not conform to Plug and Play specifications. It is good to get rid of them finally.