It’s not the hardware. And it’s not a fundamental software issue. It’s a combination of UI and trust.
From the UI perspective, Apple didn’t want multiple apps running at the same time without visual feedback. So the few apps that they allow, all provide it. A background phone call shows as a throbbing green bar at the top of the screen. Data transfer shows as a throbbing blue bar. Running audio shows as a play icon in the top status bar. And that’s about it.
So to allow more background apps Apple will either have to create a new UI metaphor or allow apps to wire into the existing mechanism. For example, allowing Pandora to wire into the play icon in the top status bar. Apple doesn’t seem satisfied with the “standard” approach, e.g., let the user remember what’s running without visual feedback and use a task list to switch/kill between apps. The Pre uses a card stack metaphor that technologists liked but the general public doesn’t seem to have bought into.
Beyond the UI metaphor issue is the question of trust. Background apps chew up memory and battery life. Both are very limited on small devices. If you don’t care how well or how poorly this is done, then you just let any app run in the background. If you do care then you need to validate that background applications don’t chew up too much of either resource. So it’s entirely possible that Apple will require background apps to be “blessed” by running them through extra validation. It’s also possible that they’ll just expand out the list of “special functions” that won’t interrupt an app. As a current example, creating an email from an iPhone app won’t stop an app from running. Perhaps they’ll expand that list to include phone calls. Right now, if your GPS is giving you driving directions and you get a phone call, you stop getting driving directions.
Apple is taking their sweet time. You couldn’t do copy and paste on the phone for two years after its release. Now Android reviewers are complaining that copy and paste doesn’t work nearly as well on Android as it does on the iPhone. Apple is trying to get the paradigm correct and work consistently and correctly everywhere. Whether that approach is good enough or acceptable is a question that consumers get to answer.
And then you throw the tablet into the mix. It has a much larger screen and a rumored new UI paradigm. And that has people guessing that the tablet will run multiple apps but the iPhone won’t. It looks like we’ll find out more on the 27th. Everything is just educated guesses until then.