Is it not partly the objective of the iPad/iPhone to complement what's there, or provide a desired functionality under a given context? Not to act as a replacement for everything....Use OS X / Windows programs and see the quality difference in software available... And no, the iPad/iPhone apps can't replace those types of software.
e.g. When recording at home I would use Amplitube rigged up to my Mini/Windows laptop, but for noodling about (while not completely abandoning my wife) I'll run up Amplitube for iPhone. While I don't expect the latter to replace the former, it does run as a great companion to it, and gives me a degree of portability that I wouldn't have otherwise.