Actually, no, if markup takes more space than content, it hurts readability of the content. Especially for such common stuff like images.

But if you don't see this obvious barrier, I will unlikely be able to explain the issue with backslashes: it's partially about the number, but also visibility - .period syntax is a smart choice as it's unobtrusive and not part of the regular syntax, and it's more ergonomic to type, so a universal win.