everything needs to be justified

This.

Not sure if this is a typical forum comment or an observation on the meaning that can be given with a single word.

  the meaning that can be given with a single word.

Very little in this case. There's a reason simple "This" comments are discouraged on HN. Having said that, I do agree that single words can contain a lot of meaning at times. This just ... isn't a great example.

Tens of thousands of people are finding some use for it, even if it's just novelty.

I could imagine yo'ing my wife to say "Thinking of you" while at work, or my brother to say "Not up to much if you want to Skype", etc.

I think they could easily start with something curious like this and then slowly extend it to something else (e.g., single word/term conversation elements where you get more choices the deeper the conversation goes).

How many naysayers were there (and still!) with something like Twitter? Yet I use Twitter many times each day.

Agreed.

Yep.