[schoen]

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.

[mcphage]

In that case, it should read "Apple betrayed by own law firm", leaving out the "its"