> Can you imagine a venue refusing entry to former clients 2% of the time just because they’ve “improved their experience”?

On the flipside, if a client enters enough venues that refuse entry to them because of something the client can fix on their end, eventually the client will probably change themselves -- "If you meet one asshole during your day" and all that.

To bring the analogy back to browsers, if a website works fine for a client, they'll have no pressure to change anything on their end -- why upgrade from Windows XP when the site looks fine in IE6? Eventually the client is forced to upgrade -- normally by their operating system. That works, but what if the operating system adds another 2 years to their end of life -- do you just hang on and hope the shim / hacks you added hold?