Well I read what's his face's synopsis on why it isn't true and have come to the conclusion that he just has a different viewpoint than what was presented (both here and in the email about this I have seen).
INDIRECTLY, the width of rail systems derived from the width of Imperial Roman Chariots. One says because it was just easier to keep that width since it had been establish and the other says its due to resistance to change within the human species. Both are probable conclusions. Neither side (snopes or the above post/email) has provided more than speculation and drawn assumptions based on perfunctory evidence.
Snopes even mentions that its Not entirely false, or true to some extent or another.