Your example is cracking me up because I know that I have brought up the rapid rate at which my DD3 goes through shoe sizes on several occasions--but I have never mentioned her putting two words together (nor do I even have a clue when that happened). Gosh, I must be a horribly boring conversationalist.
If you said it once I'd think you were trying to make conversation and I might try to make conversation back by soliciting your opinions about shoe shopping since you are probably more expert. If you said it more than once I'd wonder if you've considered there may be somebody in the room who is worried about their child growing slowly and the fact that the last three times they've bought the same size shoes.
I wonder what topics related to parenting you would advise introducing at the playground? I'm up for more interesting conversation, but sadly I often cannot think of any when I am with a group of near-strangers.
This stuff is easy for me so I'm probably being insensitive that part of why milestones dominate conversation is people can't think of other things to talk about. If you are genuinely interested in other people it seems like conversational topics would emerge fairly easily... other parks with good playgrounds, shared interest in dinosaurs, hobbies like knitting, life while half asleep, etc.
