Actually it can. Some video cards (especially by ATI) will output audio over DVI that can be used with their proprietary DVI-HDMI converters.
It's just that the DVI inputs on TVs won't accept audio so you need to convert it to HDMI first and not just any generic DVI-HDMI converter will work.
It's just that the DVI inputs on TVs won't accept audio so you need to convert it to HDMI first and not just any generic DVI-HDMI converter will work.