Get yourself a cup of tea and take a seat. Let's start with the basics. Monitors have two dimensions, width (x) and height (y). In the distant past, most monitors were of a squarish format (5:4), or 4:3 so the dimensions can be combined together to give you the diagonal:

d = sqrt(x^2 + y^2)

Making cathode ray tubes as square as possible made manufacturing more efficient, so these formats dominated. The reason for this is to scan across the same diagonal distance at the same rate (50/60Hz) took a large electric and magnetic field, thus larger coils and plates. For this reason, wide screen televisions were more expensive to produce thus were perceived to be of higher value, since you could watch theatre style movies without the "black bars".

Thus back then you could compare apples to apples when it came to marketed "screen size" and wide screens were in their own categories.

Then, a cancer called TFT LCDs popped into the market. Those low contrast monitors had a production cost that was a function of area rather than overall size. This is the key to understanding why manufacturers jumped on the wide screen bandwagon. Wide screens were already perceived to be "higher value" because of the CRT days and on top of that, only the diagonal of the screen was stated. Now, the area of a monitor is given by:

A = x * y

Let's consider the aspect ratio of a screen (it's "wideness"), e.g the horrible 16:9 you get these days. This is basically:

r = x / y

You can express the area of a monitor in terms of only its diagonal and its area:

A = d^2 r / (r^2 + 1)

i.e the trend is for the area to be a function of d^2 / r. THUS, for any diagonal size you can increase the ratio until the area shrinks to zero and still market it as that diagonal.

This explains the reason why they're selling these pieces of shit. Because they market them based on diagonals, not area. And no idiot consumer can understand what I wrote above.

Demand area measurements, you'll get sane aspect ratios.