I've seen a jailbroken 3G and once more than like 2 apps are open it slows to a crawl so I can see why Apple isn't bothering.
People keep bringing this up.
When you're talking about jailbroken iPhones using ProSwitcher or whatever - the apps it's running are actually running concurrently (i.e. true multitasking), which
isn't what Apple is even offering in 4.0. Task "freeze & resume" is not multitasking in the truest sense of the word, and allowing certain privileged apps to do minor things in the background (e.g. GPS lock, etc) is hardly the same thing as running completely different apps, in full, at the same time, that ProSwitcher et al on jailbroken phones allow you to do.
I'm quite happy to agree that the iPhone can't handle running multiple apps that each expect to have the full resources of the device at their disposal simultaneously, but I'd wager the 3GS doesn't handle this particularly well either.
The better question surely is have
you compared true multitasking on 3GS vs 3G, because otherwise you aren't comparing like for like at all.
Adding official multitasking to the iPhone 2G/3G would reduce the experience I receive while using my phone. Not something I want to happen.
How do you know that? You've got absolutely no frame of reference to make that statement at all and are just swallowing whatever Apple happens to tell you no questions asked.
If you're quite happy to be obliged to upgrade for no other reason that Apple wants you to by forcibly obsoleting older devices for nebulous technical limitations then more fool you frankly. You're their ideal customer, someone who doesn't even question their motives or statements in the slightest.
Again, true multitasking on a jailbroken iPhone isn't the same as what they're offering in 4.0. Saying "oh multitasking is slow ipso facto 4.0 task-switching would be slow on 2G/3G" is fail, it's not a legitimate comparison.