Because, let's face it: updating through the App Store is very nice when you want to upgrade without much nuisance and when you HAVE THE TIME TO WAIT FOR A DOWNLOAD, but when you want to clean install/reinstall, it's just not time-efficient. If you boot through the recovery HD and want to re-install Lion, you'll have to wait for it to download again from the App Store and then re-install. And as cool as "oh you just download it" may seem, the bottom line is that it isn't time efficient and most users would prefer to put in a USB or a DVD and have their OS there ready to install. Do you guys think that at this point Apple will go back on their word and release DVD copies or USB drives of Lion? If not, then at least they should offer on the installer menu of the final version, the option to create a bootable pen or dvd. And the installer should do that automatically for the common user.