Really? Anyone actually believe this? Every year you can count on a coach at training camp to say something like "Everyone will earn their spot onto this team." The truth is contract status matters.
7 D on one way contracts - 7 spots. But you need guys like Syvret and Greene to play their hardest, thinking they have a shot at making the team so that you can see them trying their hardest. Maybe their best is good enough to force the tem to trade one of the 7 D on one way deals? That's unlikely, but at least this way you get a better look at Syvret, Greene, etc against some NHL calibre players.
I'll be extraordinarily surprised if the Oilers don't start the year with the following 7 D on the roster (barring injury):
Now, of all the players, why has MacT chosen Semenov? Probably just because he thinks Semenov would get the most out looking over his shoulder a bit, a way of sending a message that you could be dealt/the 7th D if you don't change certain things about your game.
Pronger, Smith, Staios, Bereron are all on longer term deals, that leaves Ulanov, Cross and Semenov. MacT probably just doesn't think that kind of motivation would help Cross or Ulanov, but that it might with Semenov. That would be my guess, anyways.