You make an interesting point but yes, I think this is faulty. You see, the seed for achieving Buddhahood by receiving empowerment is not what would rippen into hell realm by not keeping the samayas. Breaking samayas is the seed that does that. That would be a new seed which could rippen into hell. At the same time the seed planted with an empowerment would still be there, just not rippened.
Are you sure about this? That breaking samaya bring negative result, not only prevent positive result.
For instance The wikipedia entry on samaya
"Khenpo Karthar Rinpoche defines root samayas as any which if violated would remove all the benefit from practicing. He defines branch samayas as any which if violated would diminish or impair the benefit of practice. He states that the most egregious root samaya to violate is the commitment to one's guru."
Well, depends what you mean by "sure" hehe... But anyway, Jamgon Kongtrul says so in his Buddhist Ethics. I can give some quotes about the effects of not keeping samaya, but first someone should tell me if it's ok to post it.
In the following quote Bardor Tulku Rinpoche also explains samaya as an opportunity more than a restriction:
And so it is indeed, however, I don't think merely not having faith in a teacher is breach of samaya.
Or scorched and, therefore, nonfunctional
You think so Bob? I had this thought too, but then I thought that once a connection has been made, it has been made. Like (I think) Namdrol once said on E-Sangha, Vajrayana is like the mafia, once you get in you can't get out.