If your camera only produces JPEG files, it would be a waste to buy Aperture, Lightroom, or Silkypix Developer Studio, since they're meant for Raw files.
I sort of disagree.
Even if you're camera only produces JPEGs, the non-destructive work flow and editing power, as well as organization, available in Aperture is still very helpful.
I wouldn't put the decision on the camera, but instead base it on what you're doing w/ the photos once you've taken them. If they are just for casual snapshots and family albums, iPhoto or something similar would be fantastic.
If you will be using your photography commercially and making money from them, then the price of something like Aperture would certainly be justified.
Another very interesting project I've been watching lately is
blueMarine.
It is an open-source photography app very similar to Aperture and Lightroom. But, being open-source, it is entirely free. It offers non-destructive work flow, and many of the features available in these professional suites, as well as some VERY cool new features (the ornithological example they provide is a good one).
It is almost in beta, so it isn't quite ready for public use yet, but I think it is an interesting project to keep your eyes on. (Again, being open-source, if you're a developer, you can change it however you like, and it is also available for just about every computer platform and OS out there).