Its only an advisory. He cant actually fail you for it. The boot (and grease) is there to protect the ball joint. If there is no boot or grease around the ball joint it will just shorten the life of the track rod end, you would probably find that the ball joint would get worn so much that it almost rattles around in the housing.
Its not a major issue but for peace of mind and OCD completeness lol, get it changed. I think i did both mine for under £25 reddies (not including the tracking).
Good luck matey.
Ant.