Agreed most others wouldn't use email as a replacement for casual chat, but its always seemed like an arbitrary choice. So many people waste so much space in emails because they treat them like letters, so the biggest difference seems to be the culture around them rather than the medium itself. If people formatted all text messages as

"Hello Dear Friend,

Here is stuff to waste space.

Here's what I actually want to say.

More extra stuff.

Sincerely, Walrus"

I doubt we would see that much of a difference between them.