You've got it a bit backwards. The reason modern console games are identified as NTSC-J, NTSC-U, or PAL is because they need a separate television to function, and they only output a TV signal encoded in either one or the other (PAL or NTSC).
When it comes to ISOs it's important to have the three categories not so much as an indicator of language, but because those represent the 3 unique discs released for most games. People don't just leave it at NTSC and PAL because there's usually a Japanese-only and an English-only release. It's not broken down just by language because PAL discs and some NTSC-U discs contain the same game in multiple languages.
It's all about identifying the distinct ISOs.