I want to see Robertson play, but let's be realistic. Dallas typically brings in the teenagers only to watch. There have been very few guys coming off their draft year that joined the Texas Stars and played. Caamano is the one recent exception I can recall, and they were out of the playoffs. To be surprised that Robertson isn't playing would be to ignore much of what's happened in the past. Also, if those "career AHLers" weren't contributing, I'd be more inclined to bemoan him sitting, but they essentially just won an elimination game for the team, and I'm pretty much OK with anything that allows Dallas' close to NHL ready prospects a chance to play deep in the playoffs.
Nyberg had a chance. He played surprisingly well his first game, and then it got a little rough. Right or wrong, it also threw off the L-R balance, but I personally don't see that as big deal. I do see it as another reason he might have come out. You're not going to sit players who are playing really well for a guy that's not quite up to speed in the middle of the playoffs.
Saying that Texas only cares about career AHL players though is pretty dramatic when Bayreuther, Dickinson, Elie, Gurianov, Heatherington, and Hintz are getting significant playing time. Some of the other veterans are legitimate depth NHLers that could and have played in the NHL in McKenzie and Flynn.