These apps:
Mail
Safari
Address Book
iChat
TestEdit
...can and should be considered integral (and integrated) to the OS. Granted, Apple does right by us users by allowing us to remove them at will and use alternatives without hitches, but I seriously doubt they will ever be available separately from the OS (not including updates) let alone as a paid-for package. On the other hand, Apple does seem to lean toward different levels for things: all hardware is "Good, Better, Best, Ultimate," iMovie vs. Final Cut Express vs. Final Cut Pro, iDVD vs DVD Studio Pro, etc.
Maybe there will be a 'pro' package that you pay for, including an HTML editor/web browser, more business-oriented chatting & em@il, etc. Sort of like the rumor that there will be more Office-like apps like Keynote in the near future. One could argue that Keynote was pushed out first because of Appleworks' complete incompatibility with PowerPoint, so we already have an Apple-branded office suite, sort of, but now we have full compatibility w/ M$ without any M$ software. Of course, now I'm rambling, so I'll end my post here.