What? That sounds really stupid. Could you provide a source?
Even if Instagram does that, they can still modify the app to take pictures properly. That's definitely not a limitation with Android.
The only problem I can see with this is people modifying the picture header to become the edited photo instead of a legitimate one (either with a rooted phone or a modified request on pc). There's not really any way for Instagram to properly verify this.
This might have changed, haven't really used the app for a couple of years.