Last month I wrote an article for Statistics Views about Triple Crown horse racing - specifically, English Triple Crown racing. Did you know there was such a thing? As it turns out, it's quite popular and has been around for a LOT longer than American horse racing. It dates back to the 1700s whereas American horse racing, at least in Triple Crown format, didn't exist until the 20th century.
That being said, check out the link above - it reveals a possible explanation why the British winners are increasing in speed while the reverse is true for the American winners. Hint: synthetic surfaces. There is even some discussion about doping in there and how that's handled in each country (it's vastly different).