It is the same Planet. But remember on Earth we have Steaming hot Deserts, massive oceans, really cold places :P, poor enviroments and rich ones. We even have factorys and stuuf! In R&C it is like the elements and themes are divided into planets (obvious!) so making a game based on one planet! Well it is R&C so there will be different places! Like Aquotos has the Sewers, The secret base and that other place with all the killer robots and In QFB Planet Merdegraw (probably spelt wrong?) they had the Caverns, Holefar Island, The Azorian Sea and Darkwater Cove! And this was a minigame!
A4O has a good chance it WILL be full length! And there will be more than usual going on in this ONE planet! So far we have only seen Two locations!? Well before i first played Tools of Destruction i had only seen Metropolis and feared Ratchet would not journey to other worlds?.. Oh how wrong i was!
Yes you will be on only one planet! Of that you can be sure. But there is more than two places on the planet. Of this you can be sure
LOL i talk with such confedence