How could a video card not have a dvi port?

i saw this one question where someone had problems with their display on their pc monitor that has an hdmi port. and the answerer said does your video card have a dvi port? dont they all have one isnt that what makes the picture display when you connect the vga cord? why would he ask that if all pc;s need the dvi port in order to even display the picture? im just wondering if he asked this because there are some pcs that dont have a dvi connected tot heir video card and if thats true then how do they display their picture then? sorry im a noob at this pc stuff im trying to learn ;D.