I've been scratching my head since this announcement was made yesterday wondering what Sony's angle is on this casting. Truthfully, I don't think there is one. Sony and director Marc Webb went for a strong actor. Andrew Garfield is not a well known actor by any means, so you can't say Sony was going for fanbase or mass appeal. Garfield is perhaps a little more known overseas, so maybe Sony was padding their international expectations, but that seems likely a very unlikely reason to make the selection. It comes back to natural ability. Just like Tobey Maguire, Andrew Garfield is a talented actor.
Boy -A and was recently the lead in the UK trilogy Red Riding.
The big question about Garfield is his age. He is currently 27 and will be 28 before the reboot will go before cameras. Does a 28 year old actor really represent a High School student? It's been done before (same age Tobey Maguire was when he did Spider-Man), but I can't say its all that believable. I'm sure movie goers are willing to overlook his age if the film ends up working out. At this point and with this casting, I'm wondering what was the point of rebooting the franchise?