Tee-hee, I love lil' cameo's like that I like the image as well! Nice definition on them Megatron seems to be all: "Get back, Optimus! The *insert ominous foe here* are coming! I'll hold them off!", with his cannon aimed forward and his arm holding Prime back
It doesn't, my dear Dolrailer. The Ride doesn't quite obey the canon, and thus allowed Megs his ROTF weapon back
I don't understand the DOTM weapon system at all... Megatron's shotgun, hand-held swords, hand held guns for Ironhide... the sudden shift in continuity is jarring, especially since Bumblebee keeps his arm cannon... oh well... DOTM is all sorts of mess.
Don't worry, it's pretty simple. In ROTF, Megs lost his cannon when Prime cut it off. His arm was replaced without an in-built weapon, so he made himself a new gun. Ironhide also lost his cannons in ROTF, ejecting them when fleeing from the airstrike. The hand-helds are his replacements. As for the hand-held swords, assuming you mean Optimus, he simply slides them out and pops them out so he can actually hold it I can get what you mean, with more of the weapons being hand-held in the third film, but rest assured the bots from the first two have their reasons for the shift in weapon-holding
It's not really a shift in continuity at all. It added some things to spice it up. Ironhide got new handheld weapons, yes. But he also had his cannons blown off in RotF. Megatron got a new handheld weapon, yes. But he also had his entire body reformatted, so I think that one's pretty self-explanitory. Optimus can slide out his sword, but he detached it in RotF as well. Ratchet, Sideswipe, Bumblebee and Starscream all retain their integrated weapons. So really, it's like a 50/50 split between the two methods.