Gravity and All is Lost are both quite a hard sell for a lot of audiences but I'm sure they also were to financiers when their directors were trying to get them made. They both feature characters adrift and alone, with limited interaction between them and anyone else.
Minimal to zero dialogue – there is no dialogue at all in All is Lost – is not something that generally has execs clamouring to put their money into a film and it's something that can also put off an audience. It's interesting, but perhaps not particularly surprising, that both of these films feature very high profile actors and I'm sure this was very important in getting the films made and also in how they will be sold to an audience.
I've yet to see Gravity, I'm desperate too, but I have seen All is Lost and I was incredibly moved by it. Redford really is superb in it too and will almost certainly be an important name in the mix come awards season.