LEO is a dense keyboard layout in the spirit of Neo and the space-cadet keyboards.
Anything that works on a standard US keyboard should work on LEO; there's no sense in breaking shortcuts people have been using for years.
Laptop keyboards never seem to agree on where things like arrow keys go, so it makes sense to provide a method of input that can be used identically on anything with a QWERTY layout. Additionally, everything important should be easy to reach and justified either by frequency or geometry.
There's no compelling reason not to provide as many characters as possible; while we probably don't need 4 bucky bits like on the original space-cadet keyboards, it certainly doesn't hurt to have some Greek letters and language-specific characters.