The thing Tassadar just mentioned, about gravity being free to propagate through other dimensions, is an interesting point.
If gravity were not confined to this dimension, this would explain why it seems so weak. Yes, Gravity is a very weak force. Try jumping in the air. All the mass of the entire Earth cannot hold you to inextricably to it's surface. Every time you jump in the air you are proving that your tiny legs are momentarily more powerful than the gravity of a multi-billion ton object. Every time you climb a ladder, you prove the same thing.
According to the 'gravity acting through more than our 3/4 dimensions' theory, this may also explain some aspects of dark matter, namely, another explanation of the need for e.g. dark matter to make our sums add up may be the gravitic influence from other dimensions making itself felt in ours.
Hope that made sense.