It was basically because in the beginning you couldnt move around unless they were vaccinated which also meant for showing. Recently they relaxed a little on all the laws as its been so long since there has been a reported case. Unless it pops up again I can't see it being useful for showing. I mainly like the fact that they can all be identified without a shadow of a doubt as my horses.
I suppose if they are vaccinated for anything else in the future that they would add those details to the ones already on there. At the end of the day I like the chips the same as I like my dogs being microchipped :)