Mostly for space-efficiency. See http://dotsies.org for a better description.

Dotsies aren't all that space-efficient, though, when compared to regular old text. For example, in this comparison:

http://i.imgur.com/Ldd70.png

I'd argue that the text on the right, in the green font, is just as readable as the dotsies, while taking up less space.

That's probably largely because the circuits in your brain have become finely honed on latin characters, after reading letters many millions of times for many years.

It's difficult to know how that image would appear to someone who was equally acclimated to both. At the moment no such person exists.

One clue might be how they compare to each other after you scoot your chair back from your computer until both have become blurry. When you get far enough away that you can't distinguish anything in the green paragraph, can you see any distinguishing characteristics in the red one? You won't be able to make them out, of course, but can you see that there are light and dark areas?

I've put about five hours in to this (The magnificent motivating power of procrastinating on something-else-you-need-to-do), and already I feel like I can identify individual dotsie words from a greater distance than I can the Roman words.

So I suspect your thesis may not be entirely unfounded.

I don't like dotsies, but if you subtract the bottom row's area where the letters aren't, the dotsie comes out to actually around 25k.

Hold on, that's really not a fair comparison at all... look at the height of each line.