I'm really trying not go after anyone's work in order to get my point across here. Just because a player is a tackle in college doesn't mean he projects to be that in the NFL. If someone said he was a tackle, that person was completely wrong. If Ted Thompson thought it, he was wrong too.
Part of being a talent evaluator is taking a player and projecting him to the NFL. There is a reason why Ken Dorsey went in the 7th round I believe and not the first-round. He did not project to the NFL. Look at Graham Harrell. There is also a reason why Brad Smith plays WR and not QB.
In the case of Colledge, you had a college tackle, who projected to be a guard in the NFL. He isn't good enough in space to play left tackle. He doesn't have the feet or the arms to do it. Frankly, I don't think he's powerful enough to handle a bull rush. I don't think he ever was. In his defense, coming out, he didn't play in a pro style offense at Boise State. Their offense is very simplified, so his learning curve was steep and they could hide his weaknesses more.
Now has he played LT for the Packers? Sure, but he's always been primary a guard. It's what they plugged him in as right away. The only reason he lined up at tackle was because the Packers had awful depth behind Chad Clifton.
Perhaps a recent example of someone who will change positions is John Jerry, who played tackle at Mississippi last year. He's playing guard for the Dolphins right now. Why? He's not a LT. He can't play in space. He's a projected guard. If he plays tackle, I think he'll get lit up. At guard, I think he'll be alright. Pretty solid starter actually IMO.
Now, Bulaga, played for perhaps the best coach in college football in Kirk Ferentz. Certainly, when it comes to preparing players to transition from college to pro, Ferentz is one of the best along with Nick Saban. So Bulaga should already know how to play LT in the pros. He's been taught it the last two or three years by one of the best offensive line coaches in football pro or college. He doesn't have the learning curve that Colledge had. Of course, this is my opinion and you could always cite someone else offering their opinion as well.
In fact, there are people out there who believe Bulaga is primary a guard in the NFL and not a LT. They might be right. It wouldn't be the first time someone was right about projecting a college tackle to guard in the pros.