Science had fared quite well so far with the assumption that the laws of physics are largely the same no matter where and when we are. There would have to be very strong evidence to throw that out. And the immediate next problem is that it actually wouldn't explain much. The immediate next question would be "why is spacetime behaving this way".
Ultimately it's just a way to say, "well, there is simply more gravity there". I was also thinking of the "why" and I'd say because when the universe expends, or initially expended, it didn't happen homogeneously. In my opinion it's more realistic that spacetime isn't homogeneous than that it is.
