Actually, I don't think this is true; Starfleet is not the main component in the Federation - every species is deemed equal in influence. Earth is the capital of Starfleet and not the Federation. Correct me if I'm wrong again, but the Federation has not once been referred to or acknowledged in JJ Abrams' Star Trek. Then again its exclusion should be of no surprise - the Federation is a narrative device used to explore the politics of interspecies relations, something clearly deemed inappropriate for what Paramount wants Trek to be on the big screen.
Starfleet existed before the Federation did, but when the Federation was formed Starfleet was moved under its control, there is no Starfleet Capital because Starfleet is part of the Federation, and the Federations capital is on Earth, it is also where the President of the Federation and the Federation Council are located.
Starfleet is a pretty big component of the federation as it is its exploration and military arm, generally everything the Federation does is through them from exploration, diplomacy, defence, etc.
The Federation is also mentioned a number of times in the first film.
It generally doesn't make sense that there are never any other ships in orbit, it is a focal point of the federation which would have ships coming and going anyway, it is where the Enterprise was built so it wouldn't have been the only one, in the previous film and throughout the series and older films we also see a Starbases orbiting. In lore Mars is also less than a minute away at warp 5 and that is a key Starfleet ship yard and defence platform for the Solar System.
For Narratives sake though the Enterprise seems to be the only one they want around, unless your a borg cube as seen in First Contact and a Breen Attack in DS9, every federation ship warping in would make little work of any trouble seen in these two movies.
There's some leeway because this is an alternate timeline, so some things might be different, but most had been decided on or happened during Enterprise or afterwards which is before these films split off from the prime timeline.