There are two sides to every coin and the potential puppy buyer needs to feel 100% comfortable with the ethics of breeding of the breeding they are seeking out.
Some breeders line breed in which the theory behind this is that due to the fact they know what they are breeding it decreases the health risks in the linebred offspring. Linebreeding is ONLY as good as the breeder who has been doing it. As mentioned above Jacquet boxers is a linebreeding kennel. I dont know them, but have heard of their dogs. Due to the fact they breed very close, they are comfortable breeding without health testing because they know the lines and the longivity of them - thats fine, but takes the right person to be 100% comfortable with this breeding practice. However sometimes they will and may have to outcross and breeding to something outside their lines esp if their lines are getting too close. When this happens you risk the unknown entering into your lines.
On the other side of the dime is the breeders who breed to other dogs with maybe some common dogs in the pedigree or none what so ever. Due to the fact you are breeding with unknown dogs, or known dogs with some unknowns behind them, they do health test to make sure that they are indeed breed and breeding to a healthy dog.
Regardless IMO when it comes to health, there are always things that can pop up - on linebred dogs, passing health tested dogs as well as dogs that were not linebred or tested. Any chance to reduce the risks of something happen IMO is well worth it and may decrease the chance of heartache in the end. Whether you feel comfortable with a linebred dog as a way of health testing or a dog that has been thru and passed tests all depends on what you feel comfortable with