I've been watching Trent's eyes a bit too. Actually I think he has improved in this regard. I see him checking multiple options.
There were a couple times I noticed him focusing on one receiver, but in those cases it was because he was patiently waiting for the receiver to come free. This was the case with the Parrish TD catch. If you watch that play closely, you see Trent spot Roscoe, then wait a beat for his route (and the passing lane) to develop. I think it takes some poise (and balls and field vision) to do that.
I've been very critical of Trent the last couple years. But so far this preseason, I've seen very positive signs. I think he is improving. He looks comfortable in the pocket (watch as he instinctively steps up to avoid the rush from the outside) and is hitting receivers in stride. I think a big part of it is better play calling and play design, but Trent looks like a real NFL QB to me right now.
(Just my, admittedly amateur, opinion)