What's the difference? (No, seriously?))
If an object of constant mass were to shrink, it would increase in density. There'd be many observable effects, such as an increase in surface gravity over time. Otherwise they'd have to (by some unknown means) shed mass at a rate equivalent to the cube of their size reduction for constant density and that would result in a reduction in gravitational pull that would be equally observable.
Also, shrinking objects doesn't explain why objects that are more distant to start with appear to be receding faster, only an inflation of the space in which they reside makes sense there.
There are probably various ways to contrive the effects that are actually observed, but an ongoing expansion of space is the easiest.
