Is This Character Secondary?

I recently finished reading Stephen King's book Under The Dome. One thing that struck me about the book was the sheer number of secondary characters. The book centers on a small town that has become surrounded by an (mostly) impenetrable dome. King takes great pains however, to talk about a huge number of the town's inhabitants. It's dizzying how many people become part of the story and have a name.

I use name as a separator because this is how I classify characters (one of the ways anyway). Let's face it; if the character doesn't even rate a name in your story, are they really that important?

For example, if I'm writing a story set in a city in current times, is there a possibility that I'll have to include a convenience store clerk? Possibly. Is this person a secondary character or someone lesser? And at what point do secondary characters become merely background description?

I bring this up because in the aforementioned tome, there are literally dozens of characters with names. There are so many in fact, that there were times when I wasn't quite sure who was who. It got me to thinking about my own writing and when an appropriate time is to name someone as opposed to merely describing them. Look at the sentences below:

Harry pushed through the door with a heavy laundry bag over one shoulder. He nodded at the owner in the corner, a disheveled man with a half finished cigarette planted between cracked lips. Looking for an available washer, Harry sighed in resignation; someday he really needed to buy one of his own. It would make Sundays much easier to deal with.

In the passage above, I merely reference the owner with only the slightest of description. He's part of the background, so to speak. Now read this alternate version:

Harry pushed through the door with a heavy laundry bag over one shoulder. He nodded at Sam in the corner. Sam must be upwards of ninety, Harry figured. Sam was the owner of this dingy place and had been for at least the last sixty years. The half finished cigarette between his cracked lips was just as dirty as the man's clothes. Looking around for an available washer, Harry sighed in resignation; someday he really needed to buy one of his own. It would make Sundays much easier to deal with.

I tried to keep excessive description out of it so that the passages are fairly similar. In the second one, I have named the character and provided a bit more detail on him. Is he still merely background or did he just get catapulted into secondary character status?

King does this with many of the characters in Under The Dome. He gives enough information to get a good idea about the character, but their usefulness if you will for furthering the story is meager at best. Is this a bad way to do things? Well, I can tell you that there were times when it made for difficult reading because I couldn't remember why a particular person was in the story (or who they were with regards to the story).

This is the point when one should question whether the character is really necessary or if they should stay minimized in the background. I heard somewhere (probably from one of you fellow writers) that if a character doesn't help move the story along, they don't belong there. I agree with that with respect to named characters. If they are prominent enough to warrant a name, they must be prominent enough for the story, right? But I do think there are times when background characters are okay too, particularly for descriptive purposes.

How do you deal with secondary characters in your writing? Do you name everyone or do you have those subtle shadows that are only mentioned in passing?