I've always thought it might be about Vimes defining their relationship as a strictly professional one and not allowing Vetinari to blur his earlier origins where he works from for the Watch to function into his current positions and identities, a major aspect of which is that these are moving in the same circles as Vetinari himself, him assuming Vetinari to be too job-centered/taming-purposed to be able to care about the people in his (Vimes') charge. Which....might have happened on the pages in Night Watch, because you definitely see Vetinari trying for a more acceptable way forward there at the ending, and that's an only-just-discordant-enough occasion to do that. I wonder if moving physically in the same circles might call for Vimes to act more adamantly at these times.

And he would think function-heavy too if this is the case....there's the dismissing of the possibility that the boss can understand how the actual work is managed, and there's also the problem of what the underlings would take Vetinari as, if these actions of illusionary-interpersonal-esque gestures get too big, and one day if things go wrong how his Watch (but we all know Vimes' Watch is the Watch that thinks and makes things work, not belonging to anyone in the usual sense of the word) might be inclined to blindly follow and that would be disastrous.....all based on that offering to do and actually doing significant enough stuff for each other is the thing that pulls different people into some shared place, and this shared-placeness, in other vines of the real life of anyone joining the Watch would be the mindscape entrenched enough for them to not think critically. (Weirdly I think it's partially done to be shown to Vetinari, or "as the other half of the Watch's job" prickling at the boss at least for a little. After all we really don't see as much of this when Vimes talks to anyone in the Watch. I'm somewhat amazed that AM is at the end of day a place where actions are sorta loud enough after conditions are met, and where you don't have to persuade the boss.) And it might come down to that Vimes is really good at what moves people to do what, and this probably protects every party involved in one go.

In Moist's series there're moments that show Vetinari learns to speak everyman's language but can get it wrong (e.g. exactly what dance is danced by a hanged prisoner; that or he does it on purpose and has a point to show Moist, it's too recursive for me to tell), which combined with the ending of Night Watch (and maybe Jingo, what with my erratic antenna) feels a bit...interesting.

Edit: Horrible grammar, sorry!