>I imagine people use + to get by character limit in the title.

What's wrong with that? The same phenomenon occurs on Twitter - people find a way to optimize every character.

Isn't an 80 character limit for titles on a modern web forum really the problem?

They should just get their threads removed then. There is no reason to silently apply that weird behaviour instead.

In fact, I would expect this to be quite rare as most people would probably use & instead.