There seem to be different conventions for headlines because they are not always complete sentences. For example, many newspapers would be fine with "Man killed

There seem to be different conventions for headlines because they are not always complete sentences. For example, many newspapers would be fine with "Man killed by unknown assailant" as a headline, or "Budget increase passed by legislature", which have the same grammatical structure as "Apple betrayed by its own law firm". Edit: oops, but that's not what this headline did. Nonetheless, the headline seems reasonable to me as a native speaker.