Yeah, I'm lucky enough to commute by transit. I usually get through at least a couple books a month, but I have trouble reading beyond the pace of speech. I'm a total book junkie so it's a constant source of frustration :)
The reason given is that it prevents you from accidentally rereading a line or skipping over one or changing lines midsentence.
This seems like one of those gimmicky approaches, and I remember being sold on this approach rather than being entirely convinced. Have you seen this before?