Speaking with Newsweek's N'Gai Croal, the two sources indicated that the Wii is actually not a very flexible system, and Nintendo even admitted that its architecture is basically "GameCube 1.5."
According to the sources, unlike the original Xbox, the Wii does not have programmable shaders and its fixed-function design is "pretty similar" to Nvidia's seven-year-old GeForce2. "The Wii's GPU has fixed functions for vertex, lighting, and pixel operations... The Wii is an older fixed function design where you have lots of operations but the pipelines are not programmable in the sense of downloading shader code to run [on them]," said one source.
The second source added, "A dev support guy from Nintendo said that the Wii chipset is 'Gamecube 1.5 with some added memory.' I figure if they say that, it must be true."
The second source did note, however, that the "GameCube 1.5" label isn't necessarily an indictment of the console. Gamers will still see graphical improvements thanks to increased memory and memory clock speed.