In a nutshell: Peter-Paul Koch claimed that mobileSafari is the new IE6, and Jonathan Rentzsch explains very efficiently why it’s not.
The only thing I have to add is this: us Web Standards evangelists didn’t get into the game to play by browser vendor’s rules; we got into the game to convince browser vendors to play by the Web’s rules: the Standards. PPK is actually encouraging that we go back to the painful modus operandi from 1999, but with five times as many browsers to worry about.
Why do we have standards? So that anyone making a new browser today could make it knowing that sites (that are built according to the standards) would just work, worry-free. It’s not our fault these vendors are making brand new browsers and crippling them, thus crippling the experience of their users.