Trevor, I get what you mean with this model. Your explanation is well put.
But I wonder, does it actually reflect reality?
Consider this proposition.
Suppose the Universe we see is actually a very large bubble or void (Giant Cosmic Bubble), which is part of the larger Universe beyond.
Suppose, the mass density within our bubble is much lower than the average mass density of the Universe at large.
The gravitational effect of this would be to mimic an expansion towards the areas of higher mass outside.
There is of course a centre to this bubble.
http://www.newscientist.com/article/...id.html?page=1
Regards, Rob.