[kbutler]

Trump elected by narrow margin

Lincoln assassinated by John Wilkes Booth

There's an implied "to be" verb, generally "was". This is very common in headlines.

The comma introduces a parenthetical phrase describing Apple, implying Apple is going to do something:

Apple, betrayed by its own law firm, countersues with gusto

Apple, ["who was"] betrayed by its own law firm, believes the best revenge is living well