I agree with you on paper there is not that much difference in ASA and the other strike calls. However, in my experience someone has worked with NCAA umpires to have them bring that hammer WAY too far forward for my likeing, well and ASA's. Are these umpires the exception? Maybe but I think a lot of different areas are seeing that forward hammer and it looks different than the approved ASA hammer. And when you are evaluating someone to the utmost level that is something to note on their mechanics. Don't we all wish we had umpires that were at the level where this was all we had to pick on them for??
One item where I would offer some advice is trying to say that ASA, NFHS and NCAA rules cover "the same game". These all cover softball, but NFHS deals with high school level athletes, minors (normally) that still "report" to an organization. NCAA deals with adult female athletes competing at a high level. ASA deals with EVERYTHING. From little girls barely able to hold the ball up to 18U Gold college skilled players on the Junior Olympic side, Adults fastpitch, modified pitch. Then there is the slow pitch world, a complete world within it's self!!
Not only is the game level and participants different but so are the umpires. ASA has everything from the dad's out of the stands up to elite umpires to worry about training and learning their mechanics. NFHS and NCAA typically have a smaller audience to work with so they are able to assume more things, and to do some things that ASA might decide just wouldn't work good for the thousands of people that they are trying to train how to umpire.
Again not trying to say we shouldn't all do the best things when we umpire, but just trying to offer another way to look at the picture. Basically what is best for the game that each rule set is covering may very well be why we have those differences in the rules and mechanics.