I find that a VERY weak argument. Capt Falcon and Ice Climbers had little canon material to work with, just like ROB. Their movesets aren't canon either.
Zelda doesn't use any of her attacks; they are used by Link in OoT.
Ganon's moveset isn't canon, seeing that his moves are cloned from Capt. Falcon.
Pit's dual swords weren't canon when he was included in Brawl.
It doesn't affect a character's chances, as far as I see it.
Captain Falcon has "falcon" based attacks, which is more character-related than "robot" attacks, so it's not as bad. Above that, Captain Falcon has personality that R.O.B. lacks, relate-ability that R.O.B. lacks, and was significantly more iconic at debut.
Ice Climbers have a hammer based moveset because they're hammer based fighters, and again they don't lack in personality and etc.
Zelda didn't use farore's wind or etc, but we knew she was magical from OoT. Simultaneously, Zelda was kind of a character that "had" to be in the game, as she is the namesake of the entire LoZ series. There's a difference between improvising on a moveset for a character that was in the thoughts of practically every potential customer, and improvising on a moveset for a character that very few knew about, let alone thought of it for smash. And even beyond all that, making up "laser eyes" because "it's a robot" is far from having Zelda use Link's magical items.
Yes, and I think Ganon's lack of a character-related moveset has been a bother to the smash community for a while, right?
True with pit as well, but a variable is Sakurai designing the game.
Above all this, they didn't have to improvise for pretty much every move like with R.O.B.
At least with C. Falcon, he has "falcon attacks," and despite a lack of creativity, at least "hammer attacks" work with the Ice Climbers, but with ROB, it's pretty much just "he's a robot. Do robot things." That's like saying, "Link is humanoid. Have him punch/kick/etc."
With R.O.B., you're not going to find a YouTube video with 100k views about the history behind their moves in SSB like you would with Pikachu, or Link.
One major thing smash does is it represents multiple franchises, so if the moveset doesn't reflect the character form the franchise, then that's pretty poor representation.
It's not that R.O.B lacks personality, or has an exceedingly basic/non-personal moveset, or that he wasn't as acclaimed/popular/etc to warrant a slot as much as whatever next character, it's that he has a, what I'd say, noteworthy extent of all these problems, which makes them compound. Yes, C. Falcon lacked an inherent movepool, but he had personality and a little less movepool issues than R.O.B.
They just gave him robot things because he's a robot.
That's what I'm saying. He's a representation of robots, not of "R.O.B.," because there's nothing to represent of R.O.B. He's "just a robot," not a unique Nintendo character.
Neither did Zelda, yet they improvised her moveset based off of Link's magic.
All the Ice Climbers did was jump and hit with their hammers, yet they made a moveset for them.
Canon really doesn't matter.
Dammit, Fal, you covered my points. Okay, um... ZSS barely has anything to work with, yet they made a moveset for her.
We already knew Zelda was magical, I posted about ICs but I'll add that at least they have ice related things as well.
I'd like to think that Canon matters quite a bit. If not, don't you think it would help declone Toon Link by replacing his sword with Judo skills?
As for ZSS, that's true. But again (not at the same scale, though) she was highly demanded and anticipated, like Zelda was in Melee, so she "had" to be in.
Well, a lot of R.O.B.'s moves involve moving its arms... well, the original Robotic Operating Buddy for the NES moved its arms in order for you to play Gyromite and Stack-Up.
I don't think that's very strong. If something has arms, and it wants to do something, it's gonna move them. That doesn't separate rob from anything else that has arms. 
I'm one of the few people who were delighted when he was revealed.
