I'm a dressage nut myself, and can tell you that you must be looking at the wrong dressage, as Spyder said, if you think it's about having the horse in a high, stiff frame.
As a baby you don't want to put them in a high frame! You are asking them to lower and stretch those weak back muscles to build them up, keeping their back soft and swinging. As you go up the levels in dressage, the degree of collection increases, so pretty much in your initial, lower levels youre looking for horses with a lower head carriage, soft swinging back and everything nice, tidy and flowing. As the levels go up, judges want high head carriage along with higher degree of collection. By the time a horse is at Grand Prix the head carriage is quite high, but this is due to the level of collection they are at. If the work is correct, they will be taking the majority of their weight on their hind legs and their forehand will 'lift'- lower head carriage is good for stretching their backs and getting them prepared for collection, but it's not posisble to be in a level of high collection with the head down near their chest!!
In the case of pure dressage being different to eventing dressage. 100% different I don't enjoy watching eventing dressage unless it's a top class comp and then only the riders who have put alot of effort into getting correct dressage work. I find eventing dressage to be very tight, flat and just not correct.