You can compare a car's length to a truck's height; the units work out--whether or not its useful to do so is a different story (if you're playing tetris with cars and trucks, it might be very useful!). In particular, we can (and probably do) measure the magnitudes of the media's biases (pro-business, pro-government, progressive) and compare them, and it's very useful, for example, if you care about media bias and want to know what kind of pressure to apply to get the most bang for your finite political capital.