Is it deviation though? It's certainly related. There's the old saying of 'practice what you preach'. To me it appears that Osho didn't do that, but used rationalizations to justify indulgence on a mega scale.
You can go through Osho's book, 'Awareness : The key to living in balance'. He explains the reasons for his methods.
Abstinence is great in a pre-industrial world, but in the modern industrialised world where food, and primary human needs are available in plenty, with plenty of wealth compared to the past, along with changes in fashion that stresses more on baring the body, along with cheap and easily available pornography, the human mind is obsessed with sex. Sex scandals were common even for the monks and clergy in the past as well. I have read of a pope who had many illegitimate children. This is the era of short skirts, miniskirts and tank tops.
Osho felt that for such a mind, also stressed out greatly due to the tensions and strains of the modern world, could relax by shedding inhibitions, along with conditionings that could bring guilt and repressions which actually make the mind more unconscious.
Hence his teachings on indulgence and gibberish so as to express completely the hidden tensions and feelings within the mind and purge it out .
He had also advocated the method of meditative awareness in the beginning itself for those who do not have a highly conflict ridden mind.
But the basic philosophy of tantra or yoga remains the same, that is of the inevitability of gaining happiness of a permanent nature from sense-objects. Indulgence in them will also bring out this truth and the more sensitive and intelligent one is , the more this truth will be evident to him or her.