Folders don't let you do that either. You can't have folders simultaneously organized by Event, Date, Photo Type, Subject, and so on. (Not without manual shortcuts cross-linking photos to multiple other folders, and that would be a big kludge and/or tremendous work.)
If you change systems, getting your originals will be easy. Tell the new system to import from the iPhoto folder, and have it suck up all the photos. Windows has provided that kind of feature for a decade. You'll lose all your iPhoto-specific meta-data, most likely, which will suck. But that's a problem with any photo-organizer.
The caveat to this, is that iPhoto keeps both original and edited photos. This is really great because you never lose a photo to ill-considered editing. The downside is that if you migrate, you could have lots of pseudo duplicates, getting both originals and the edited versions.
But I'll ask again, in all practicality:
What do you mean by organized? As you say, "I'm half-assed organized, with emphasis on the word following half" Are you really now going to change your long-term behavior, and create a super-organized system of all existing photos, and keep it up on all future photos? If you've never done this before?
Or would you be happier to have a program hoover up your photos, do some basic organization for you, and let you easily do the big-deal sorting with a little effort? This is not sniping, this is my hard-learned practicality over the years of getting hyper-organized for a few months and then realizing that's me and falling back to old habits. Now, I try to pick solutions true to myself
In five years, you might decide to change systems. But who knows what you'll have in five years. I can only say that I've been happy so far with iPhoto, and much happier that I no longer think about organization, beyond "these photos were taken in September" and "these photos were taken during the same weekend vacation".
If you do want long-term compatibility, look at cross-platform organizers, particularly: Lightroom and Picasa. That might give you better peace of mind for future options.