So in my opinion there is no reason for most people not to take a Reiki class in person. If it is to be then you will find the way and the means. Now having stated my position, what about the claims made by those doing and receiving alleged distance attunements. I am going to introduce some things to consider from the teachings of Edgar Cayce. I reference Cayce because his beliefs and teachings parallel Reiki in many ways.
All healing comes from the infinite.
The Usui System of Natural Healing is a method of accomplishing this, but not necessarily the only method. With the exception of our use of symbols to fortify our healing abilities, the teachings of Cayce and Usui are much the same. The healing ability we all have within but need some external inspiration to bring into being.