My sink is oval, 16 inches at its widest, and a 12 inch spread would look very strange. Even the spread on my kitchen faucet is only 10 inches. I don't think I've seen anything referencing over 8 inches for a lavatory sink. Mine do follow the curve of the sink. I don't notice it as curved as it isn't very much. A straight line would put the handles further from the edge of the sink than the spout, and I think that would look odd to me.

I also have a small oval sink, spacing is 8", and the holes follow the curve. I actually bought a prefabricated granite top, so this spacing must be pretty standard.

12" is WAY too far apart! (Unless you had one of those ginormous 2 or 3 foot sinks? LOL)