You are correct about Orthodoxy allowing cremation where required by law, as is the case in Japan, and memorial service.
The reasoning is that cremation constitutes desecration of the body. There is really no easy or tasteful way to dispose of a body. American Indians would leave the body to be mauled by wild animals. Eskimos did the same thing. Hindus cremate theirs. Egyptians with money used to be altered chemically so as to last forever. We allow the body to rot. No matter how you look at it, the body is destroyed one way or another.
Cremation is natural. It involves no human hands or dismemberment, or chemical alteration (by injecting dies and preservatives into the body, after it has been drained of fluids), etc. It's dignified.
But the Orthodox Church will never accept it.
For the record, the Catholic Church disallows any disposal of the body that is intentionally done as a symbolic denial of the resurrection of the body. Such are all the dispersal methods. Of course, no physical act can prevent the resurrection of the body, but any burial whose symbolism aims at denying this truth is sacrilegious.
At the same time, cremation in itself is allowed.