I'm not entirely sure I follow why you feel this is significant. At least in the US, we tend to measure viewing distance in feet and diagonal screen size in inches, and those are both measures of length. It's not like the two axes are "feet" and "fluid ounces."
Even if it was fluid ounces, that's still not a problem - A line chart of my account balance would have Euros on the y-axis and months on the x-axis. It's still a meaningful chart though...