DXOMark Low-Light ISO score in practice?

I see that the low-light scores of A77 is about 800, while the old glorious A580 has about 1100. I kinda remember the scientific explanation about the portion of light beam split by the A77, but I'd like to ask how relevant is this index in practice.

I have a lot of experience with using an A580 with an f2.8 lens in low light: it's perfectly usable but not great. I recently tried an A77 in similar conditions (not an entirely fair comparison because the A77 had a very good lens on it), and I had the /overall feeling/ it was way better; in practice with the A580 I end up deleting a much larger percentage of pictures.

My blind guess is that most of the difference is caused by the AF performance, and the DXO index measures just the abstract sensor potential.