It's the Americanized version of the Japanese super deformed style toys.

You could blame the Marvel figure collectors for getting Hasbro started on the kick. At one point there was plans for figures based on when Mojo turned the X-Men into cute little kids in the X-Men costumes. Fans saw pictures of what might have been and since Hasbro had picked up the Marvel figure rights they wanted to cash in. The Marvel Super Hero Squad sold well enough and they were cheap enough to produce that Hasbro figured why not cash in on other lines.

It's not really something for every fan since you need a good bit of silly to your collecting taste to really enjoy them.

For me they are fun for being wrong on just so many levels. A super cute ruthless terrorist organization just doesn't seem like something anyone ever should have come up with. It's like giving guns to Hello Kitty characters or something.

That and with Transformers you are way more likely to get characters in the Robot Heroes line than in any other line so I've got a much better collection in the Robot Heroes line than I could ever hope for in the classics/universe line.