it is not quotes that are lagging.
it is very simple. Often times the specialist is holding a huge market sell order for example and people are willing to get out 5-10 cents lower then the bid because they KNOW the specialist is about to pull his bid down a lot more.
Yes you can consider this an arb, but if the specialist decides to pull his bid down 50 cents, you will be screwed. I have seen it happen a lot of times.