Actually, another postscript to what I said, wouldn't it be great if the Aquarium came with just the 3 fish and then when they purchase it, then the other 18 fish come in as an automatically-downloaded fish pack?
It would sure make piracy more difficult if it were impossible to download the full version from SereneScreen.com without a valid keycode!
About Microsoft not worrying about service packs; I think they have more than enough servers to compensate for the entire world downloading updates...
Well the service packs are huge, 100MB or so. But it's better than having the user download an entirely fresh copy of Windows every time there is an update. 500MB per user. Ouch!!
External self-installing fish packs is a good thing.
And Jim, before you say this would be a tech support nightmare, look at the system Winamp uses. When Winamp first runs, it creates a file association between files of type .wsz and itself. When you go to Winamp.com and click on a "skin" for Winamp to download it, it automatically does a "Run this file from its present location" or "Open this file". Winamp runs, accepts the wsz file, and auto-installs the skin.
So if you wanted to make sure you had the most up-to-date Aquarium, either you can use the built-in upgrade system, or you could have download links to each of the fish packs on SereneScreen.com with no install process! Click on a fish pack and it automatically adds itself to the Aquarium.