I'd say SSB has been trying to branch out from "Nintendo all-stars" to "video games all-stars". If you look at the list of third-party Smash characters it's pretty much a who's-who of the biggest names. I'm pretty okay with this.
Also man between Snake and Cloud SSB can now claim more Playstation star power than Playstation All-Stars itself ever could.
First off, agreed to the second point!
With regards to the first point? Sakurai did state he'd allow 3rd party characters if they were on an exceptional level. Cloud was basically the only character who was not in Smash (if we include Snake in Brawl) that was on this level.
Cloud is the most oddball choice for 3rd parties but not because of "he's not big enough", since that'd be a blatant lie, but more that his home game, FF7, never appeared on a Nintendo console. Granted, he did appear in a few games like Chibirhythm and the upcoming Final Fantasy Explorers, so it's not like he's compeltely absent from Nintendo consoles (thus why it doesn't feel like a cheat!), just...yeah.
MAKE NO MISTAKE: This is not a complaint. I think it's a neat, if unexpected, pick. Just kind of saying Cloud probably wins the biggest oddball reward. All the other 3rd parties feel far stronger attached to Nintendo, save Snake who isn't in this Smash. Still pretty cool inclusion nonetheless.