The Mac’s quite famous for refined, simple and highly usable design. While some of the design cues found in the original Mac may still work just as well today as they did back in 1984, the single menubar doesn’t.
Having a single, unified menubar back when no one had 27″ iMacs or dual-screen desktops was probably a logical, zen-inspired approach. Nowadays, the single menubar can be an annoyance. As for remembering shortcuts, well, that isn’t always practical for apps used infrequently.
I did something about it: MenuEverywhere. Click on the screenshot for more information.