Just more genius from Nintendo regarding the GBA. Personally, I'd love to get the GBA and hook up, but I don't have time to even start most of the GC games I have laying about with the features they have, let alone GBA bonus goodies, replaying the old Marios and Zeldas, 3 new Castlevanias, Metroid Fusion, the E-reader......ye gods, thats way too much.
It would be a much different story if the GBA link fundamentally changed gameplay or was an absolute requirement. Is anyone really of the opinion that MP or WW are not worth the price of admission as they are? To most of us, these are two of the finest games ever made - the GBA connectivity just provides a little extra to round out what is already a fantastic gaming experience (kinda like the extra "crunchies" in the bottom of the Long John Silvers bag - I dunno where the hell they come from, but man, I love 'em).
The fact is Nintendo doesn't have to add the GBA features to GC games. With sales through the roof on GBA/GBASP, its hardly necessary and I can't imagine it makes much difference in GC sales. I don't think its a case of getting less for your money; on the contrary, it shows Nintendo is willing to put some thought and effort into expanding the experience and rewarding loyalty to get you MORE for your dough.
In the immortal words of Sgt. Hulka: "Lighten up, Francis."