At the risk of offending Will's sensibilities,I wouldn't consider any of those pictured masterpieces.
The wisteria is certainly a horticultural accomplishment and an incredibly showy bonsai.
The cotoneaster is the closest to a masterpiece as has been posted yet...but not quite, in my opinion.
Walter Pall's maple is mediocre compared to many other of his works.
The Pacific Rim photos are excellent examples of very good bonsai,but not identified as to how they originated.The very best...again in my opinion....had the patina of age unlikely to be achieved without a great deal of time,where ever and how ever they originated.
Connecting a famous name to a tree does not make it a masterpiece.
Just so Will doesn't think I'm picking on him

...let me say that I agree with him that a "masterpiece" and/or at the least,a very good bonsai can be started by using nursery material.I think that "the very best bonsai in the world" (as in the very best bonsai in the world are yamadori)as Jason would say, is a phrase that is useless.Some people like Picasso and some like Rembrandt.Some like rugged ancient gnarly conifers and some like graceful broadleaves.As I've stated before...I think the best trees in the world are the ficus from Taiwan.It's a cultural thing

.
Unlike Chris,I find the discussion interesting and worthwhile reading.Unlike many,I won't try to convince anyone that I am right and they are wrong.
I also will not post any of my trees as examples of great trees grown from nursery stock or(in my case) cuttings.If I WERE trying to convince anyone that you could grow great trees from nursery stock,so doing would defeat my purpose.
Everyone should remember that even yamadori started as seedlings.With enough time and effort...and skill...nature's harsh treatments can be duplicated.
andy