I thought about the "preparing to run" scenario, but he get's in that pose like he's prepared to block debris, even turning his head a bit, and then when the shield drops, he kinda' lowers his arm, and THEN prepares to run.
The pose in-front of the tanks was a shot done by one of the artists specifically for a background as a "gift" to halo fans before she left... it's not really an actual movement pose. However, I kinda' get what you're saying, and I guess he had to do SOMETHING while the shield was over him.
I can't think of a pose that'd be more appropriate, I guess, it just seemed unnatural the way he got into the pose, rather than just leaving his throwing arm down. It's not like I expected him to scratch his ass while in the shield, I guess.
The shield grenade definately generated the shield.. you could see the parts of it floating out of the top of the grenade itself when you look at it frame-by-frame. I just wonder if it somehow worked WITH his suit, considering how the shield balanced around him, instead of around the grenade.
By claiming that the ad didn't reflect gameplay, and the fact that the X-button feature may actually change (as though they've got a couple of ideas they're trying, instead of being locked into one..), I think they've shown us two possible x-button moves that they can easily deny..
For example, if the X-button is a sprint button, and the shield is removed, they can say, well the shield was too powerful so we removed the shield grenade. Or, well, the sprint was just for drama, he'd look silly sauntering into battle.
Instead, we hear nothing and have two items that stand-out as being clearly impossible to do in Halo 2.