B.3.1 - Simple and straightforward language

B.3.1 currently says:
Use the simplest and most straightforward language that is possible for the
content of your site. [Priority 2] 

After much discussion, the consensus seems to be that this is a P1 item
that needs an explanation.  However, I am having trouble providing an
explanation that doesn't sound like an author can write this one off.
help!  here's what I have so far:

Use language that is as simple as possible and appropriate for the content
of your site. [Priority 1]  While it is difficult to define "simple" in a
way that makes this checkpoint easily demonstrable, ....