Comment by notpushkin

Those are services that depend on Apple servers. If you also make a service, others can’t pirate it (they’ll have to set up their own server, which means it’s not really your service now).

Of course, this only works if you secure your server side properly. I remember using cracked versions of Wolfram Alpha for Android back in high school and those worked like a charm. I don’t think they lose a lot of revenue though.