There were a lot of spots held back in the MN events this year. When you look at MN's growth rate, we'll probably be in the neighborhood of ~220 teams this year, with open capacity at our own regionals of ~240 spots. It's a really tough job balancing open access to play against diverse teams from across the globe with ensuring access to local area teams that may not be able to travel... I do not envy the RD's (ALL RD's!) that job.
That said, for teams local to any given regional, when you see that many spots that have been held back for the waitlist, you can probably sign up with a high confidence of getting in off that waitlist! And if you are in doubt, you can always contact your local RD's or Senior Mentors to get some direction! Just look up their contact info on the right side of the page here:
http://www.firstinspires.org/about/contact-us