You're correct, iOS apps can only handle schemes but now whole URLs. On Android, the system can intercept any URL and pass it to the app (http://instagram.com/blahblahblah goes to the Instagram app, for example), which means web URLs can open in apps instead. On iOS, you must use a dedicated scheme, which means links from the web don't play nice with apps.

Opener attempts to fix this by mapping web links to app-specific links.