It is against the law to sore horses. They send agents to as many shows as they can to check for it, but some still get away with it and some of the "inspectors" are dirty. Some still do it and/or get away with it.

The flat shod walkers are not sored, as they are trying to have a forward rolling gait, rather than a high stepping gait, but if you want to show a walker here in Utah you have to pay an extra fee to have your horse checked before entering the ring or you cannot show. They don't even show Big Lick walkers around here. It's disgusting and I look forward to a day when this does not happen anymore.

http://www.walkinonranch.com/CNN.html

This is a video link showing people soring horses or trying to cover it up. You can see the horses are obviously in pain.