Hore is part of the leadership group in the ABs (along with McCaw, Mealamu, Thorn, Carter, Smith, Muliaina), and Nonu has been the best 12 in the world and an outstanding performer for the ABs for the past three seasons. Neither have disciplinary issues within the AB set-up either on or off the field. Hore is known to enjoy a beer but is nowhere near the rabble rouser he once was in in early playing career.
Now admittedly, they might be willing to toe the Henry line in order to be in the AB squad and they may not have a similar fear, hunger factor for their home franchise, but it really takes a fair bit of balls to remove 2 current ABs from the squad (Nonu wasn't exactly playing poorly either). Both have strong personalities, but are considered genuinely good blokes. Nonu befriended SBW on his first AB tour last year and apparently went out of his way to get him acclimatized, which is hardly the sign of a trouble maker. Hammett may have found it tough to stamp his authority on the squad and change "the team's culture" with Nonu & Hore's on-field and locker room presence but I'll be very surprised if it emerges that either were disruptive.
Hammett received full board backing for this move but the board had to either fully support their coach on such a matter, or fire him. Bottom line, I expect this to be just a case of Hammett wanting to do everything his way and only his way, and that was proving difficult with two such strong, personable and influential players. One would have though that a good man manager would have been able to deal with such issues (making assumptions here), but Hammett clearly sought and was granted exactly what he want. Next season, he had better produce strong results or his coaching career will deservedly be cut short.