Look in the data summary (PDF below). "Other Products" which includes the Apple Watch grew 'only' a billion year over year.
And Other Products 2015 explicitly does include Beats Electronics.
And wikipedia (https://en.wikipedia.org/wiki/Beats_Electronics) says that Beats revenue in 2013 was $1.5 billion.
If all that is right -- and it may not be -- then that implies that Beats + Apple Watch < $1b revenue, which would indicate that something is very wrong. Indeed, it would imply that something is SO wrong that I doubt I have the facts above correct.
EDIT: Duh, thanks thedaveoflife, obviously the $1.5b for 2013 Beats is an annual number, not a quarterly one. And of course the iPod numbers are presumably shrinking. That explains it.