Take for example, the PC.
The IBM Personal Computer was a relatively simple design that has remained pretty much unchanged since its introduction. Now there are parts of the PC design that just show how painfully legacy it is (IRQs tend to be my biggest peeve), but people don't drop it because something new comes out - they do what all computer hackers (Note: hackers, NOT crackers) do - they go around the hiccup to solve the problem.
Computers have not, until recently, been built for "Do this and upgrade every six weeks" (Todays big exception is graphics cards and hard drives, but you get my point).
The internet definately hasn't been like that until certain large companies starting screwing up all the standards to suit their own software, for whatever nefarious reasons they were found guilty of.
Now does this mean that new technologies shouldn't be pursued? Of course not. I like to see pictures when HTTP'ing - of course, Flash completely blows goats on my 233mHz K6, but my perfectly adequate NetScape 4.79 renders 95% of pages JUST FINE thank you.
But, like many above have mentioned, instead of saying "To hell with the other folks, hey, I didn't need that 60% anyway", you should make up your website to work with older browsers (Note: Again as said, it doesn't need to look the same - it just needs to be readable), and then you can pile all your junk on top of that so that the people that can view HyperReactiveHelloKittyPluginX applets can see how good you are at masturbatory webpage juicing.
So that, in my half-page nutshell, is my opinion on redesigning the web so the poor suckers like myself can't use it.
-- Alexander Widdlemouse undid his bellybutton and his bum dropped off --