Lack of Standards in Modbus

I am about to teach a class on Modbus to customers. Most of our customers see computers as a tool (This is a good thing TM), and are not programmers. So I have to explain how this very old standard does not cover current use and there are dozen's of different ways to use Modbus. The basic standard has not grown since the 70's. There are no standards for bytes, 32 bits, 64 bits, floating points, bitfields. Even byte order is not followed by some vendors.