It's not about the name or an idea of an "opera house" in the sense of perception, but rather the structure of one. The seating of an opera house isn't like the seating of the venues Apple normally uses. It has balconies with optimal / priority seating to aid visually and acoustically. I have a hard time believing that a company like Apple, that focuses on visuals and acoustics, a company which can pretty much have an event at any venue they want ... picked an opera house randomly / because it amused them. That they didn't think about how it would be presented in such a layout, but yet put so much attention to detail in the visuals of the invitations.
"Wall Street Journal, we don't care if you arrive late, you have to sit on the third floor, first come first served."