Why do backslashes prevent alias expansion?

Question

In the first part of my question I will provide some background info as a service to the community. The second part contains the actual question.

Part I

Answer 1

Just for completion, here's yet another way to suppress alias & function lookups (by clearing the entire shell environment for a single command):

# cf. http://bashcurescancer.com/temporarily-clearing-environment-variables.html
env -i ls