The cube turns everything into Decepticons because Bay and his writing team are a bunch of morons who could care less about the actual Transformers canon.

The ice cream truck twins were nothing more than comic filler. Their ability to change into those two new cars, is an inherent one to all Transformers. This was shown in the first movie too. All they need to do is scan the surroundings for a suitable piece of machinery (or bodies), to imitate. Of course in the original series, this was an ability limited to Teletran 1, but whatever.

The Fallen/Palpatine dude, is from the Dreamwave comic series. I've heard good things about that series, but I never really got into it. As far as I'm concerned, the Transformers were originally created by the Quintessons (those 5 headed judge things from the animated movie), as detailed in the original series. The more religiously inspired story of Primus and Unicron, can eat a dick for all I care.

As for the teleportation thing, and why Jetfire was a crotchety old man with a cane; well, see point #2.

It would be interesting to hear Swyndle's take on the film, as he is a way bigger fan of the franchise, than I am.