Its the small things like a slick icon that makes all the difference
for your app. You want, for instance, my co-worker to walk past my
desk, and for your app's fancy icon on my phone or in my mac's dock to
catch his eye.

He'll ask "what's that app" and then you've got word of mouth
marketing right there.

It's actually happened to me before - it's important for us developers
to simply put some effort into our designs.