I believe the intent of this law is to prevent the introduction of an unwanted species into a body of water. It has happened a lot. In Maine, fish such as pike have been put into lakes that held native brook trout and have decimated the population. There are many instances where this has happened. People who were well intentioned (or not) have taken it upon themselves to stock these fish illegally not realizing the damage they were doing. It has happened all over the country. Ever hear of the Snakehead? They theorize that someone had some of these fish in an aquarium and once they got too large released them. They are all over the place now and they displace native species.
Those people who have transported live fish to be weighed in then released broke the law, even though they meant well. The reason they got away with it is because there was no EPO around. A lot of the weigh stations are just sporting good stores and have no power and probably no desire to make an issue out of it.
So how did 9.4 get around it?
Technically he broke the law.
I can understand the reasoning for the law. It makes sense. However, If I am ever lucky enough to hook and land a 9+ lb fish.... I refuse to kill it. I will have my live well with me and bring it to be certified and return it to the waters that I caught it in. then tell anyone who asks.... Oldham!!!
Here is a list of all the certified 10lb + bass caught in Mass up till 2007 I believe. If you click on the image it gets a bit bigger and clearer