It may benefit such an event to signal selectivity even if all invite-requests are granted.

Also, so many people just crash open free events (with beer!) that applying even the slightest seriousness filter could boost the event value a lot for its intended audience.

There are plenty of all-comers networking events, too -- it's not like the bay area tech startup community is either fragile, requiring gentle encouragement to finally grow, or exclusionary, starving for fresh blood.