Details are important, not so much because of what they bring to the table, although the smallest touches can often create an experience that would be degrees less enjoyable by their absence.
Which is why I was stoked to find Little Big Details, a really cool collection of UI touches that add an extra something to the user's experience. Check out the video example of Bandcamp's nifty little trick that turns a graph into a game of Defender (you can play it here if you want).
What is it about the little details? It's not what they give so much as what they portend. Someone who takes the time, care and imagination to impart that extra detail to the degree that it improves the experience of the end user is unlikely to be shoddy elsewhere. So in a way, that little touch is a signal that the rest of the product has probably been given plenty of attention.
Maybe that's why they seem so important and give you so much joy. They're a little ratification that the rest of the thing they're attached to is probably pretty sweet too.