While I have never heard of hotwiring a horse to get the piaffe, I don't doubt that it has been done. I think if you look hard enough into any and all riding methods, you'll find some bad. EVERYWHERE. There are always cheaters in this world that will go to abusive lengths to get what they want.
The OP doesn't say anywhere that all dressage riders use abusive training techniques so please do not attack, They've left the door wide open for a really great debate so let's stay on topic.
I do not agree with the statement that dressage horses are "the most trained" or talented horses. There are so many horses that are trained in so many ways, western reiners, western pleasure, dressage, even some of the higher level jumpers have some pretty extensive training.
As for dressage, it's pretty impressive to watch, it isn't easy to do, the rider has to have a really good understanding of what they are doing. I agree it has really changed over the years. We keep asking more and more of our horses and really forcing them to pull all of their talents together.
What are you riding now Ponyboy?
"Be a best friend, tell the truth, and overuse I love you
Go to work, do your best, don't outsmart your common sense
Never let your prayin knees get lazy
And love like crazy"