I don't see this as being pretentious (not saying you do, by the way), but I see this as just wanting to "belong" in a group of like minded people. It's pretty natural and happens in countless ways across all walks of life. I will certainly "like" a wrist shot of a watch that appeals to me, but to be honest if you asked me 5 minutes later to tell you who's watch that was that I just liked, I would not likely be able to tell you...
Wanting attention and needing it for validation are 2 different things. Not sure anyone needs it here, but I'm sure we won't complain if we get a few likes for a wrist shot.
Since I work alone all day, and rarely post wrist shots here (or anywhere really) I'm pretty sure I buy the watches I have for myself, not for anyone else. Okay my wife sees them (not that she pays attention) and the neighbours might see me out walking the dogs, but as I'm bending down to pick up dog poop I doubt anyone is paying attention to my watch...
"Hey Al, what do you have on today?"
"Well John, it's my GO PanoReserve with the exquisitely finished Cal. 65"
"Sniff..sniff...what's that smell, Al?"
Cheers, Al