Could you give a link for that comment? It appears that fella' is talking BS, but maybe some details got lost and I'm not familiar enough with North American rail terminology. But assuming it's not my failt, my reply would be:

It is true that US rail and wheel profile is different from the European one, but you solve that by changing both (after all, when the German ICE made a demonstration tour of the US 15 years ago, its wheels were replaced), and it is not a function of high-speed or conventional. (After all, as others said, many French TGVs continue their travel to destinations along conventional lines, say Paris-Bordeaux, which is high-speed less than half-way, only until Tours.)

The grinding rate I know about is a measure of maintenance needs: how much of a line has to be grinded a year to correct rail surface errors. As such it has nothing to do with compatibility with conventional lines. (And on some heavily-used TGV lines, the grinding rate can be not just 30% but up to 50%.)

_{*Lunatic*, n.
One whose delusions are out of fashion.}