If you always optimize your attention towards whatever is most immediately compelling, you'll wake up one day and find out you don't really know anything.
As the article says, it takes more than 30 second to divine whether or not a conversation is going to go somewhere interesting, and if you stop paying attention at the drop of a hat, it never has a chance.
I think that's an older-generation thing. If you go 30 seconds without getting to the point, of course people will think that you don't have one.
I don't know where I'd be without those conversations.
I don't think that valuing relationships by how useful they are to you "right at this moment" is a very good way to go about life.
The point is - in my opinion, it's equally rude to pull out a smartphone in the middle of a face-to-face conversation, as is to approach someone "fiddling with their phone" and expect undivided attention.
One of the rudest behavior I encounter is people suddenly coming to you and interrupting in the middle of your IM conversation, demanding undivided attention and refusing to accept that you're in the middle of a conversation. IM is not e-mail, it's often as time-sensitive as voice, and quite often that IM conversation is much more important than whatever the interrupter came with.