Why is there something rather than nothing?

This question, related to the existence of the universe, is one that, as an atheist, I've been asked on more than one occasion. I have two responses. The first is: why not? And the second is: why God?

Why not?
There is a subtle, and almost hidden, premise here. The premise is that 'nothing', whatever that may be, is actually the default position, and that 'something' is the exception rather than the rule.

I don't think that premise has much weight. Consider the following points:

• Nobody knows for sure what happened before the Big Bang. We don't know, with any certainty, if there was indeed 'nothing' before the current universe came into being, or if the universe came from some previous 'something'.
• What is the definition of 'nothing' in this case? If one speaks of 'nothing', are they referring to an absence of everything, including matter, time and space? It is claimed that God created these things, so I would assume that a theist is talking of a kind of 'pure' nothingness, an absence of everything that we understand to be the physical universe.
• Related to the point above: in all of human experience and history, nobody has experienced or demonstrated 'pure' nothingness. Even in a vacuum space and time exist. In other words, if we consider all our knowledge and all our experience, we can be pretty sure, with a high degree of certainty, that something exists. But the same cannot be said for 'nothing'.

In other words, the idea of nothingness is simply an abstraction. There is no reason to presume that a state of 'nothingness' is actually the default position, if it has even been the case, or even if it is possible. Why should we consider it at all, then?

Why God?
It seems that apologists unwittingly trap themselves when they ask why is there something rather than nothing. Their basic premise is that it is impossible to get something from nothing, more from less. Thus, God has to be the missing link that explains how something came from nothing. But what about God? If the universe (which is something) requires an explanation, then doesn’t God (who is also something) require an explanation too? The question can thus be rephrased:

"Why is there a God (i.e., something) rather than nothing?"

I wonder if the apologist can provide a possible answer to this question.