well, basically.. vrml technology was too infantile to really be of much value yet, and generally 2d navigation is still more efficient and intuitive then 3d navigation for most things online. Not to mention, to make any kind of 3d environment that looks as good as a nicely designed 2d site one would need way too many resources. Also it doesnt help that most if not all 3d web solutions require plugins most people dont have. Flash and pdf plugins are extremely well adopted by the masses but thats not the case with the various 3d plugins.
Maybe 3d web graphics will get a boost once browsers support OpenGL or things like that.. but personally i see more use in svg to open op graphics possibilities for the near future then i do for OpenGL.

Screensavers; people use their computer too much to bother for screensavers. Computers lost their gimmicky appeal, i guess it reduces peoples interest in software that only gets used when the computer is not being used. It used to be gimmicky just to see a computer do a screensaver, these days it takes much more then just a little graphic to impress us.

As for the skins.. i dunno.. maybe grahpical standards have gotten too high for many people to bother making skins anymore. maybe they consist of too many components for people to bother making them, or maybe they're just outta fashion? lol

Bryce does so well because its simple, easy to use, and stable. Also bryce got lucky because simple and easy to use programs with a small price tag have been consistently popular throughout the past few years as 3d software became more popular with the amature graphics enthausiast. While time progressed bryce fell behind on its competitors, but it also became cheaper and the amount of people looking for entry-level 3d apps increased, thus keeping it in a healthy place in the market.
I dont think there has been a bigger plan for this since the beginning considering that bryce switched owners twice now..

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