Q: Who should be invited to a shower or bachelor/bachelorette party?
A: A sampling of people who are invited to the wedding.
Not those who are on your "B" list, not those whom you don't want at the wedding - but you want their money and gifts.
Your showers and pre-parties are not a gift-grab (well, okay, showers technically are). To invite someone to a shower or stag/hen party, and then not include them on the big day, well, that's just impolite.
I will allow for one minor exception: when a celebration is thrown for you by someone else, and is either without your knowledge, or it's understood that this is a context in which it's okay for you to not invite them to the wedding. Example: the girls at the office throw you a luncheon shower, but it's already been made clear that you and your intended are having a small, family-only ceremony. Or your mom threw you a shower (ahem) and invited distant family friends whom you hardly know. (ahem.)
(Variations on this theme are welcome.)
But to expect others to throw you a bachelor/bachelorette party and then exclude them? Rude and unacceptable.