I think the big missing point here is that it can take up to 48 hours (or even 72 hours) for every ISP to reset their cache and get your new destination. Sure, I can always run dig or even dscacheutil manually to wipe my computer's DNS cache, and I'm pointed over at OpenDNS and Google's DNS so I don't really have to worry about DNS caching issues, but my customers aren't.
I can't say "Hey look, it works on my machine so you must have a lazy ISP, your fault!" when they say "Hey it's been 6 hours and my website doesn't work yet", the proper answer is simply that in most cases it takes up to 48 hours to work.
I can't say "Hey look, it works on my machine so you must have a lazy ISP, your fault!" when they say "Hey it's been 6 hours and my website doesn't work yet", the proper answer is simply that in most cases it takes up to 48 hours to work.