Yeah - but Epic is the only ship I know of where if you fail to make a reservation there is a very good chance you will miss a show entirely.
BMG appears five times on that cruise (I think) - BUT - usually the first four are fully ticketed by the first day of the cruise.
If you miss your night, then you have to hope you can stand in line (for an hour) and get a leftover seat. Now, I believe it is not that hard to get in on standby, especially if you arrive early.
The problem is that no regular cruiser thinks that way - it is something you have to KNOW about Epic before you get there. The guy probably just asked about tickets each night and was told they are were all gone, but he didn't think about standby.
Also - if you want standby its a separate line, and you better get there early.