"This change won't affect a number of groups such as Pro Networks and Non-Profits."
Assuming this means that most of the small community-driven groups will be unaffected by the change.
Still, this is clearly a communication fail, as well as a cardinal sin for usability:
By charging users to RSVP yes, they are literally putting a tax directly on a key engagement activity for the whole site.
I also agree with the comment that Meetup has done a poor job of improving itself. The "design facelift" they did 2 years ago negatively affected the growth of our group, and they haven't added much value since then.
A better approach would be to take 15% of ticket sales done through the site in a way that could improve engagement and revenue.
Meetup may have a well-deserved PR hailstorm for this.