I agree with HansTWN.
One of the biggest reasons traditional postal services are called "snail mail" is because it's so much slower than e-mail.
But reading on a paper book is no slower than reading on an eReader, so the term "snail reading" would not be appropriate at all.
If there is to be a term, it should emphasize "tradition", "old age", and such, not speed.
Nothing catchy comes to mind... but then I was never good with catchphrases and such.