Here's one thing, one thing I want from iOS 7.
In iOS, if you get mail, you get a number badge. If you view some of it on another device or the website, the number updates. If you view all of it, the number goes away.
If you get a text message, the number changes. If you check your messages on another device, the number updates.
Same with the Phone app and voicemail/missed calls.
But if you get a Tweet or a FaceBook message or reply or otherwise a notification of some sort, and you check and change the number from somewhere else, the number does not change. It does not update.
I don't see why those apps can't have updating numbers. It's not a matter of not being able to set the number to what you want as a developer, because I've seen plenty of apps that do badge with ever changing numbers. I don't know if it's Apple's problem or FaceBook/Twitter's fault, but someone needs to fix it. Especially since FaceBook and Twitter are so well integrated into the OS anyway. You'd think they'd have noticed this "problem". It's all about presentation and logic really. If my FB app has a number, I expect it to have an update to show me. It's Human Interface 101. I really hope they too noticed this and are either working on fixing it or talking to the developers themselves.
Now yes, the first three apps are built-into the OS, but Twitter and FaceBook do have some integration, so I'd expect them to work the same. Plus as I mentioned I have had apps that have been able to change the number to whatever they want. Or so it seems.