Dear Petofi,
I have an original ring (I got the fancy gold band which seems to be decorated with filigree-like ornaments of either flowers and leaves or bows and ribbons) and I also bought the MPI re-issue several years ago. There is a noticable difference, as you have mentioned. The original is indeed beveled to a point and then the plastic "stone" is flat. The re-issue "stone" is rounded, not flat.
Petofi, you have me looking more closely than I ever have at my ring. There is another easy-to-see difference between the two. Beneath both the original and re-issued rings, there are oval shaped holes that allow you to see the black "stone". These ovals are crossed by a horizontal gold bridge which appears to be soldered onto both versions. The bridge on the original is thicker than the re-issue and extends closer to the outer edges of the ring. (This bridge always bothered me as a teen because it prevented the ring from resting up against your finger.... it raised it about an eighth of an inch....NOT like Barnabas'!) Plus, the oval opening in the re-issue is larger than the opening of the original.
Also, more tellingly, this underside of the two versions of the rings has two very different patterns of, for lack of a better word, crosshatching. The original has very fine vertical lines that run the entire length of the ring (not being seen below the attached bridge). The re-issue has a different pattern of crosshatch, more like the feathers of a bird's wing.
And here is the thing I can't believe I'd overlooked on my original ring! One of the little round balls, the one closest to where the band attaches to the ring, is actually a tiny screw. It appears to be a phillips head screw. This really blew me away that I had never noticed it. Unless.... my original ring is not in the best of shape. I made the mistake of wearing it to my first DS conventions and after so many times of putting it on and off, it became worn. So, perhaps this is not actually a screw but a damaged ball? But, it sure looks like a tiny phillips head screw! Can anyone verify this on theirs?
A word of warning about wearing your rings. As I mentioned above, wearing the ring at the DS conventions was fun but it took a toll. Eventually, a crack developed in the pliable band. I stopped wearing it but eventually it broke. Someday I plan to have it repaired but in case some of you have been tempted to wear yours, be careful! (I've never worn the re-issue so I don't know if it's any stronger than the original or not.)

SDP