That is true, even a very famous orchid like B. nodosa known for its wonderful fragrance can be scentless, although I doubt it is as common as scentless delenatii or maliopense.
I had a few, (still have one and a bunch of hybrids) and while they were all scented, the degree was variable.
It's best to buy one in bloom to be sure, but who buys nodosa at night? hahaha