I didn’t think it meant that, if only because it was her right hand, and it’s the left hand that traditionally wears the wedding ring. I didn’t think to compare the ring to older pics though, which is why I found it interesting when Duncast mailed to point out a change — Leah wore the ring on her pinkie in the cinematic reveal, back in 2008.
I’d say this has even less significance than the left hand vs. right hand question. As we saw during the Cinematic Panel at Blizzcon, Blizzard makes as many changes and iterations on the designs in the cinematics as in their games, and from the dates showing on the border of many WiP shots, they were mostly done in 2009 and 2010; long after that June 2008 preview cinematic was completed. Someone at some point thought the ring would look better on her ringfinger, and would probably help balance the hand a bit more, with some sort of demarcation on a central finger.
Or maybe she’s actually married. Secretly. On the wrong hand. To
Diablo Azmodan. And now she’s going to have his demon-baby, etc. Spoilers!