"Not to sound totally ignorant, but how in the world do you do a session through email or chat? Do you make your sub whip himself while reading from a screen?"
Domination and submission are intensely mental experiences. There is a mindset one must occupy to inhabit either the D or the s role. For many individuals, submitting mentally and emotionally is a far more important and meaningful experience than allowing another individual to strike them with any type of implement, and they achieve trust and submission through (shocker!) written correspondence with a partner of their choosing.
This type of submission (and what I believe should come before any physical submission) ensures that the submissive and Dominant understand one another thoroughly on a mental level because, hey, in verbal exchanges on the interwebs, understanding is pretty much all you've got and, in many ways, all you need. Sure, you can have pictures and have a basic idea of your partner's dimensions, but this does not make or break a mental D/s relationship.
Interacting within a D/s dynamic is not predicated on body position, interpersonal distance, or physical input. A man two thousand miles away could be completely submissive to me without ever having met me or actually kneeled in my physical presence. How? I've owned his mind. He's invited me into his brain, his desires, and has willingly and consciously submitted to my will.
Last time I checked, the will was an aspect that was neither dependent on touch nor dictated by distance.
For many individuals, cyber play, writing erotica, and engaging in long-distance relationships are their preferred methods of expressing their D or s identities. For personal or professional reasons, they believe that this is the safest or least messy way to maintain their vanilla lives while not denying their kinky selves. Who are we to judge another person's expression of sexuality?
Writing, chatting, taking orders, or simply checking in once a month through an e-mail can work for those who seek a purely verbal interaction. Personally, I find these types of interactions wildly fun, as it takes lots of brains and lots of imagination to make them work well.
In summation - it doesn't take a paddle, it takes two brains interfacing to make a D/s connection or to hold a session. Imagination trumps physical limitations, every time.