imported post
I was thinking about this and although Seafair is a private organization and has (my assumption)rented or otherwise procured Genesee Park & the Stan Sayres Memorial Park, the strip of dirt/grass between Lake Washington Blvd and the lake isn't either of those. I'm not sure if Seafair can rent that space from the City of Seattle, and therefore it might not be subject to the same restrictions that they can put on both of the rented park spaces. IANAL and don't know what the rental agreement looks like, so you may not want to chance it, but if you avoid the parks you might be okay. Otherwise, I'd take them at their word for enforcing the no weapons policy.
Also, it has beenmentioned to me that because of the numbers in attendance (100k+), the whole site falls under some special Homeland Security event classification. I'm not 100% on what that means, but it sounds like the law enforcement personnel have a few more powers granted to them in those conditions.