Let's see, in 2003 there was:
Keyboard LaunchPad 1.0
DesktopX 2 (and now 2.1 which is a major version too)
WindowBlinds 4
The new WindowFX stuff
The new IconPackager
Theme Manager (a rewrite from WinStyles)
IconDeveloper 1.0
SkinStudio 4
Now, two of the programs were completely new to Object Desktop. IconDeveloper is $20. Keyboard LaunchPad is $10.  That's $30 in new software that you never were promised but that you got because you have Object Desktop.
Add to that the discounts on things such as Aquarium and other suites and you're nearly at the $34.95 upgrade price. And that's ignoring DesktopX 2, SkinStudio 4, WindowBlinds 4 and the other significant updates that came out.
Stardock had to pay thousands of dollars to license the fish in Aquarium. It wasn't cheap to do. And fish swimming on the desktop is not something we ever implied or promised would be part of Object Desktop.  AND YET we still gave away a few of those fish for free as DesktopX objects in the library here just for Object Desktop users.
Like Paxx said: DesktopX users could make their own aquarium. We even provide some of the fish for Object Desktop users.  But since we had to license the models for those fish, someone has to pay for that. If it came as part of Object Desktop, then we would have to make a cut somewhere else and that wouldn't be fair to those Object Desktpo users who have no interest in the aquarium.
It makes sense that those who are interested in the aquarium be the ones who help pay their share of the licensing costs for getting the fish.