I've been browsing LessWrong less often as of late, and I believe that one of the reasons is because I don't want to get all excited all over a new insightful LW post, only to discover that it's a meetup in a city that I'm not even in.
And for newbies to the site in particular, they're not going to see all the awesomeness of this site if they simply look at the frontpage and think it's a community just for meetups.
I'm sure meetup discussions can go somewhere prominent. Maybe a separate section can be devoted to them.
I think the main reason meetups are on the main page is that some people don't look at the discussion section, and we want as many people to see meetups as possible.
As a data point to the contrary, I now mostly look only at the discussion section, because there is nothing on the main page except the meetups.