Napoleon III, and Louis-Philippe before him both took great pains not to appear as autocrats. They spent far more effort on winning the support of the public and having at least the appearance of a functioning constitution. Each regime also understood who its base of support was, and played to it.
The other difference, and this is important, is that each of those monarchies came to power with public support. Charles X was a foreign imposition, a man who owed his position to God- as manifested in the Holy Alliance backing his brother- and not to the people.
Charles X wasn't merely concentrating power in the King and his cronies, he was doing so with no support base. Even much of the elite was against him.
The Bourbons could have establishing a regime for the long term- Louis XVIII did a surprisingly good job of that, after all. But the July Ordinances were the response of a government who thought it could deal with structural problems with a crackdown, not a long-term strategy.