Strangely enough, I have an Android tablet (Polaroid PTAB-800) that does it exactly the way you describe it. EXCEPT that it doesn't, as the OS and all installed apps need to fit into the dedicated space. If your apps use any extra space for app-specific data, it's stored in the OS section, not in the user section, which is brilliant unless you want to have more than two large apps installed at once. On the other hand, I still have a full 8gb of space, and can add an SD card for more storage, but can not get more app space. If you root the PTAB-800 you can *technically* run apps from the SD, but it tends to glitch badly more often than not, which cost me several months of progress in Valkyrie Crusade.
It's a first-world problem, and one of the reasons I will never buy a cut-price tablet ever again, but it also points to why Apple did what they did. I'd love to see the plaintiff's reactions when they realize that they can only have a handful of apps installed in their "separate OS partition", but they still have 16 (or 8, or 32) GB left for porn and MP3s.