The DIAGONAL measurements of the screens is not directly comparable because the two screens have different aspect ratios. Tell me, which screen is bigger, a 30inch 4:3 (non-widescreen) TV, or a 30inch 16:9 (widescreen) TV. Please don't say they are the same.
In the world of TV's, they are the same size, DIAGONALLY. In your example, they are just different dimensions/resolutions. What if I told you that you could have a TV with 16:9 yet, one only has a resolution of 1080x900 resolution and the other has 1800x1200 resolution. You going to argue that they are not the same size?
Also, if you remember back years ago and I can't remember how many years ago, there was a class action lawsuit out because manufactures of Monitors were claiming they had a 20" screen (Diagonally), however, the actually size of the DIAGONAL was less then the 20", something like 19.1", because the manufacture was including the "CASE" that held the monitor. I believe there was a ruling (could be wrong, that was in the 1990's or something like that), that they must display the correct size of the actual screen DIAGONALLY. And that was how Screens were and have been SIZED... DIAGONALLY.
Also, in comparing a Windows 8 tablet to the iPad is like comparing an Apple to an Orange. While they have similar shapes, they are different beasts all together. If all I wanted to do was play Angry Birds, Candy Crush, other games, Read/Compose e-mail, play the piano, drums, then I would use the iPad, but for my business, I use the Surface Pro, because like the commercial showed, it can do so much more and it does.
When I saw the commercial for the first time, I thought wow, it's PC vs MAC all over again, but it's PC throwing the punches this time. Guess it hurts when you are on the receiving end. But I am not here to argue that the iPad is better than a Windows 8 Tablet or vise versa. I just don't care. I use what works best for me. I have both PC and APPLE products in my house and work, and they are used for what they specialize in.
Take it for what it is, but I found nothing wrong with what the commercial advertised. Nothing that Apple has not done to MS in the past.