*blinks*
...Why isn't this the default?
That site shows pretty good before and after images, but the "before" rendition is just stupid and I don't see why anyone would design web browsers to do that.
The page doesn't even discuss any other viewport settings or suggest which websites it is or isn't appropiate for, just "You should include the following <meta> viewport element in all your web pages:". If it's something everyone should include everywhere, then it should be the browser default. I am not going encourage poor browser design by catering to it.
That's not just the viewport changing, though.
I can see why putting the effect line on a separate row would be convenient on narrow screens, but it's not appropiate for all cells. The "Data points / Last Confirmed" is really not useful if it's not right next to the data (admittedly, I'm being slightly naughty by not explicitly arranging them in a table and instead trusting them to line up because each line has constant height - doing them the proper way would require a lot more coding to make the cell borders work properly, though). I see that you deal with it be just hiding that column on narrow screens, which is understandable, but I don't want that to be the default because then some people wouldn't notice it exists at all, and the column is important because it gives a gauge of reliability (if there's only two data points, take results with a grain of salt). Plus, that column is pretty narrow (unlike the effect line column), it should be able to fit.
I guess I could just make the effect line a separate row for everyone more easily using colspan="2". I kinda like the current layout, but it does have a lot of empty space on the left side.
I've tested it and found that the current layout is still readable at 640px width (by just shrinking my browser window, or by tacking a width value to the table itself) if the font size is shrunk to about 67% of my computer's default, though on my screen 640px is still approximately 15 centimeters, so I can imagine that font being unreadably small (even though it's still rendering properly rather than pixellating) on a mobile device. (EDIT: Though while your quote used 640px as an example, this site suggests 320px is a more typical resolution for phones. I don't see how that could fit even in single-column format.)
Incidentally I also tested that on my computer that the viewport meta seems to be completely ignored, as it doesn't do anything when I set the viewport width to something either larger or smaller than my browser window. That's probably a good thing, since according to the image at the bottom of this page, actually forcing the viewport width to equal device-width on windowed systems is completely nonsensical.