I'm assuming you're in the US because I am. If you're not, please let us know. If I'm not, and I'm having a good time, tell me after the party.

I suspect you might need to talk to a lawyer if there's no one in your local area with experience. I think it's likely a local zoning issue. Most workplaces have to be accessible, but not even all of them, and physical abilities may be required for a job.

People have the right to work, but entertainment's different. While I'm pretty sure there's no federal law requiring wheelchair access to movie theaters, bars, restaurants, or music halls, I can't say about local laws. I'm pretty sure people's houses aren't ever considered public venues, and money-making doesn't matter. If you were having a party to sell plastic food containers or lingerie, it wouldn't matter. It's a private residence, no matter what goes on in it

The bigger issue is that maybe this person has just been locked out of one too many places and decided to get militant about it. This certainly isn't going to help them get invited to a lot of other things. Consider how disappointed and frustrated you'd feel. Maybe talking to the person to try to work something out would be better than fighting about it. Even if there's no solution, the attempt to find one would be better than virtually slamming a door on one soul who wants to be at the concert and wants others to care that they can't.

In the end, if nothing gets better and the disgruntled person remains disgruntled and spiteful and decides if they can't get there, they're going to ruin it for everyone else: houses are private property, mailing lists can be private, the events can be private, and bye-bye problem. I'd give the rational way a try first.