You stated:  "It means caps are legal on the steer axle except if they are used on a farm vehicle.  Caps are never legal on the steer axle of a farm vehicle."

That is not true.  The code says they are not legal on a farm labor vehicle.    When you remove the word labor, you change the meaning of the sentence.  Kind of like if you take the sentence "blue lights may only be used on authorized police vehicles" and remove "blue" and then say there is a law that says lights are only legal on police vehicles.  

Apparently I misunderstood your comments regarding the tx code. 

edit:  I am not sure what I was misunderstanding there.  Basically the answer to eddiedry's question is "yes"