A dumb TV still has a TV tuner, so they aren't equivalent.

But unless you plan on plugging it directly into an antenna for OTA broadcasts, they are basically equivalent.

- TVs don't need anywhere near the same level of display quality. They are viewed from ten feet away and do not render small text, so they don't need as clear a picture. They also don't really have to go over 30fps, and latency is less of a concern. Basically, they have looser constraints in many ways, making them cheaper

- TVs have a plethora of inputs of many formats

- TVs have remote controls

But I doubt you could buy a 60" glass front monitor for the price they sell TVs :)