The flaw in this argument is of course that Christianity and science are not trying to explain the same things.
Wrong. The bible gave an account of the creation of the universe which is completely wrong. The religious are forcing their outdated ideas into the school (as in intelligent design). This is the overlap of science and religion and this is where the battle is.
Are the gaps getting wider? There are plenty of places in the modern universe for God. For example, dark matter, dark energy and the quantum vacuum. Certainly this should give the atheists pause (how do we know God is not concealed in dark matter - we know very little about it). However, it is not a place I'm prepared to consider because science moves on and dark matter may not even be thought to exist in a few years.
This is dishonesty. Where in the bible did it say that god is in the dark matter? This is making up of an excuse to make the irrelevant god looks possible. It is not. Why god needs to hide in the dark matter?
The argument is that as science advances and more is explained the need for God diminishes and so the Christian faith is superseded on all fronts.
So Sissons actually knew the correct interpretation of "god of gaps" but deliberately chose to look elsewhere in order to protect his blind faith.