Ha, I had no idea. That's kind of a problem, yeah. They REALLY fixed that with San Francisco which has, by my count, a crazy 18 cuts across 8 variants, counting only generic sans serifs.
Eh, in a UI font though? I appreciate the lack of italics in the UI of my system (which is running Mavericks, so has Lucida Grande), it keeps the menus clean and there are better ways to add emphasis where truly needed.
Not necessarily in the UI. But, as the default font, it was the one that a lot of apps would er... 'default' to. So, if you were writing a text document in such an app and then went to make some text italic you'd realise it wasn't available so would have to change fronts.... which could then affect the layout, no. of pages required etc.
