On the "siri shouldn't confirm reminders if they won't actually happen", I agree with you, this is a bug. Siri should either complain in this case, or silently re-enable whatever you disabled. I filed this through a developer channel.
I can tell you why this happened, though. People have complained over the years that non-system apps (think like what OmniFocus is to Reminders, or what Google Maps is to Maps) don't have the same level of "built-in-ness" that the system apps do. The result of this feedback is that Apple has made more system-level privileges available to third-party apps so that they can have more feature parity with system apps. Rightly or wrongly, the decision was made to let the user edit some of these permissions (like Background App Refresh) because perhaps you don't want to use Reminders, or you want to use OmniFocus instead. Meanwhile Siri is just inserting reminders into a database without a lot of awareness of whether it's OmniFocus or Reminders that will ultimately process them, or whether they're running or have the right permissions. That's how we got here.
On the multitasker behavior, this is debatable. Specifically, there is a dispute about what this multitasker is good for.
- Does it exist primarily to let you switch between applications?
- Does it exist primarily to show you apps that are running and allow you to quit them?
Arguably, people use it as both, and arguably there is a lot of overlap between these two things. But there are sometimes where these ideas don't overlap, and so you have to make a judgment call about whether to design it for one case or othe other.
I think when you are in that situation (where you must do one at the expense of the other), you should favor the displaying and quitting of running apps. This is because:
- There are other ways to switch between applications, like arranging them on your home screen and tapping their icon or using Siri. There's no other way to quit apps.
- If your goal is to scan and find some application to launch, these other interfaces are way better and more productive. The multitasker is really only good for switching to an app in the five or so that you've recently used. It doesn't order them consistently; there's no muscle-memory; you have to make a lot of gestures to even view the app you're looking for, etc. It's just not a good interface for looking for apps you used several days ago.
- Having a lot of apps in the list doesn't really matter for the task switching case, because we've already established that you're only using the first five. The fact that Reminders appears way over to the right in the list doesn't really impact the usability of the task switching behavior, so it does you no harm to leave it open. The only reason that Reminders would appear near the front of the list is if you opened it recently, and in that case it's even more logical to display it in the list.
So for those reasons, I think that the multitasker behaves better in iOS 7 than it did in 6. It's really only good for switching between a few recent apps, so there's no harm in letting the list grow quite long.
Finally, I would say something similar to what I said earlier about the Background Refresh feature. There is some desire here to let the user use third-party apps for reminders. What you call a "critical system service" is another person's "how do I turn this off?"
I can't tell you how many thousands of complaints I've gotten that "Reminders works in the background... why can't your app?" And I have to explain that it's because Reminders (and Maps, and Phone, and ...) all have Secret Voodoo Powers that no third-party developer can do. In iOS 7, we've taken a step towards leveling the playing field and making first-party and third-party apps behave more similarly.
For example, people in this thread have learned for the first time that quitting Reminders stops it from working. Maybe now they will learn that quitting the apps that I write stops those apps from working too instead of expecting them to magically continue to work. Being consistent about stuff like that for first-party and third-party apps sets much more realistic expectations about what third-party apps can and can't do. If users quit Reminders and it still works, then they start expecting that same behavior for OmniFocus and Evernote and Things and they try all of them and leave a string of 1-star reviews in their wake complaining that none of these apps behave like Reminders does.