Just to clarify (this bit me last year): many people put their email addresses in the "about:" field of their profiles, so that other HN readers can email them. Here, pg is referring specifically to the "email:" field, which isn't publicly viewable but is the canonical email address used for YC announcements.
In sum, the problem is that
a lot of applicants haven't put their email addresses in their profiles
and the solution is to
put your email address in the email field [and not just the about field].
Some people put their email only in the "email:" field, without realizing that it is invisible to others. Putting it in both About: and Email: would be nice, so that we (the other readers) can send a personal email if needed.
In sum, the problem is that
a lot of applicants haven't put their email addresses in their profiles
and the solution is to
put your email address in the email field [and not just the about field].