I live in Australia and about half our beef production is apparently grass-finished. I believe what we get in the supermarket is more likely to be grain-finished, but I've definitely bought steaks with the telltale grass-finished yellow fat from Woolworths before. My understanding is that it's more about rainfall and seasonal feed than the particular flavour of one or the other.

For the record, I also think calling grass-fed beef gamey, metallic, and saying it's unlikely to be popular (like the top-level reply did) is an overstatement. The most prominent thing is the different coloured fat. The taste isn't hugely different, probably because our grass-finished beef still gets enough feed.