by regular stone, do you mean just something from the case in the local brick & mortar store and not a diamond chosen for it's specs?
My DH proposed to his ex with a ring like that. It was just a pretty ring. I think because of their age/lack of diamond knowledge, they just picked something that looked nice & was as large as they could afford at the time. And then when that relationship ended, she gave back the ring.
When he started hinting about rings to me, I made sure he knew what specs I was expecting. He was able to get a trade in at the same store, otherwise I would probably have asked for a cartier 1895. lol Mostly because i liked the setting, not because I thought it was a "superior" diamond, though.
My diamond is actually the same carat weight as the trade-in, except the that it's set in platinum, whereas the 1st ring was set in 14k yg and mine is leaps and bounds improved in color/clarity & cut. I don't think the 1st ring even had specs for the cut/polish/symmetry.
I