alt Hacker NewsTo be fair, the alt-input is a generalized system for inputting Unicode characters outside the set keyboard layout. So it's not like they added this input specifically. Still, the em dash really should have an easier input method given how crucial a symbol it is.
It's a generalized system for entering code page glyphs that was extended to support Unicode. 0150 and 0151 only work if you are on CP1252 as those aren't the Unicode code points.