Actually, by the traditional definition, they were still middle class, as higher classes were defined by more than just money (royalty, political position, etc.)
Paul Graham goes into detail on this very issue in his "Mind the Gap" essay: http://paulgraham.com/gap.html
Wealth has always been a big part of it, but throughout much of human history, wealth didn't create class; class created wealth. Your access to the monarch or ruling body granted you certain monopolistic privileges and land, from which you derived enormous wealth. But the wealth was the byproduct of, and not the generator of, class. (In fact, many extremely wealthy people, such as successful merchants and traders, were nevertheless denied elite class status because their class ranking had been fixed at birth).
This equation was turned on its head to some extent by the industrial revolution. This was the first time in history when the wealth generated by industry and trade began to dwarf the wealth generated by land ownership and agriculture on a massive and undeniable scale -- thereby wrenching power from the nobles/landowners, and placing it in the hands of newly minted industrialists. But even in the following century, it took a long while for wealth and social class to become thoroughly decoupled, and then reassembled in a different way.
What's happening now in America is that we're once again returning to a system where parentage and class beget wealth, which fixes class, which then repeats with the next generation. There are always notable exceptions to the rule, and these exceptions are held up in support of the "American Dream." But they are very clearly the exceptions. (And, in a surprising many of those rags-to-riches stories, a closer examination of the events behind the narrative often reveals that the "rags" origins were exaggerrated to varying degrees).