Joe L,
Summed it up very well. As any good pistol smith worth his weight in salt will attest, the holy grail of accuracy in a semi auto is consistent shot-to shot-lock up of the barrel. Consistency = accuracy.
We get calls every day asking if we recommend the barrel bushing. You may be surprised how many times we "don't" suggest it. If you only shot very short distances, i.e. 7 - 10 yards, the difference is not significant, in most cases.
When shooting at 10 yards plus, the difference can be significant. As Joe L pointed out, the factory hand clearances the barrel to the bushing in the final assembly phase, and this can vary from very good to extremely poor.