I agree. The RJ45 physical connection standard is a definite weak link. Surprised someone hasn't worked out a solution, yet. Other than that Ethernet is really good at data transfer, but I still think it's iffy for real time control.
Ethernet protocols have developed and gotten to the point of near domination in plant networking including high performance motion control, and there really is not a lot of competition. Device networks is still an area in the factory where there are options like CANopen, etc.
Al, this is another example I have seen in Design News of Ethernet being used in the industrial world. It is interesting to see how widespread ethernet's adoption has been. I worked with the very earliest implementations. Ethernet won the battle in the computer connectivity world because of its flexibility. It has been taking over the large scale telecom carrier world. Now, it seems to be making significant inroads in the industrial networking world. Not bad for an open standard.