If the "I launched the wrong app" problem is really why Apple did it like this, then they're optimizing for a rare use case at the expense of more common use cases.
There's also the use case where you have a related apps on the same screen or in the same folder. If you open a Facebook app, how likely is it that you'll want to check out Twitter next? If you get done checking the NYT headlines, might you want to open CNN or Flipboard next? Sick of Angry Birds so you open up Words With Friends? These scenarios don't seem that unlikely to me, but the "go to screen 1" behavior breaks them.
Even so, presumably, if these apps are important to you and you open them regularly, you have them on the first or second screen, so making the home button take you to the first screen doesn't seem like a huge additional burden.