The http://i.ytimg.com/vi/4h9w-MV8RMY/maxresdefault.jpg hints that Codsworth can be upgraded. You can see a dismantled Mr. Handy on the left side by the door. This shot shows us that we can customize weapons and power armor, along with revealing skill books/magazines, bobble-heads, and the perk chart. I don't think the Mr. Handy pieces being there are a coincidence.
Plasma weapon, paint job and some programming?
I'd expect the army version to be armoured as well of course, but you're right there isn't a whole lot of difference.
I believe the Quake Con information has mentioned an Attack Dog perk. Im guessing it may be tied to .. Perception or Agility? Not sure. Either way Im guessing Dogmeat will get perhaps more agressive with a much stronger bite/more hp?
I not aware that the companions are involved in any perk getting or level gaining. They just get better I guess. I just remember hearing YongYea going on about the Attack Dog perk. as I assumed the only person who could get the perks was the character, i just assumed it fed off perhaps perception but im guessing strength might also be there too as a possibility.
Not saying im right there, but its just a guess its based on one of those 2 stats.
Its entirely possible , we might find a Dog trainer in game who can train Dogmeat to be a nastier dog.