Registration and Email Subs

This may be answered somewhere else but I can’t seem to find the right way to phrase my search to find it…

Can someone point me to the difference between – and a way to combine – the core WP User Register functionality and the Jetpack Subscribe by Email functionality?

I find it utterly confusing that the two are not tied together: users can register without subs or sub without registering. That seems unnecessarily complex when, in my experience, I want subbed, registered users – one login, one set of subs, one control system!

Thanks in advance for any pointers.