Sounds complicated, is simple. When you get to
meta through the link in the
help drop menu, you can't get back to
main the same way. Therefore I suggest adding a 4th item to that drop menu on meta sites, which could read something like:
Get back to the main site
You're on Meta site now
(Excuse me, English is not my first language and it might use some more clever help text.)
It was pointed out before on meta.TeX.SE that this assymetry can be confusing. I'm posting the request here since it should apply network-wide.