Ok let me clarify. By default, apps don't interact with each other on a lower level. However, there are ways to make apps interact. Like giving access through SU (Titanium Backup, etc), or related apps can be designed to use the same user/group (like I've seen for the dialer and contacts apks), the shared prefs function, services or some other method idk. It's only in these cases I think the crashing of an app with that extra access would affect another related app.