Unacceptable how? They had no responsibility to do otherwise. They no longer wanted the employee so he was removed immediately. Are they supposed to give him notice even when he has no value to them?
It's unacceptable on the level of treating people with appropriate acknowledgement of the inherent fuzziness of society- employees need time to get hired elsewhere, and employers need time to find a replacement- thus it is courteous to give notice on both sides of the relationship. By not acknowledging this fuzziness of human society, one is also giving the message that people will not be treated with what is the standard understanding of human dignity.
Sure, if he has no value to them, the company has every right to let go of him and hire someone better. Doesn't mean that they have to do it as if their worker is an unfeeling mechanical automaton whose sole purpose was to spend his existence slogging for the company, and that he somehow failed in that regard. A little empathy wouldn't hurt.