When you read GhostOfHeraclitus' new story, "A Canterlot Carol", you might imagine that he wrote it in a mad dash of inspiration, like Coleridge writing the opening to "Kubla Khan".  He did in fact write almost all of "Twilight Makes a Cup of Tea" that way, only under the influence of some particularly-nice tea (I assume) rather than opium.  But I have an inside line on ACC, so I can point out some of the deliberate story structure choices.

Let's look at an outline of the story.  SPOILERS EVERYWHERE.

Scene 1: Dotted's office.

Humorous opening with Santa Claus

Scene 2: Spinning Top's office.

Continuation of Santa Claus humor

Introduction of Zebra / Blueblood subplot

Dotted insists that Spinning goes home for Hearthwarming with her family

Dotted has plans for Hearthwarming

Scene 3: Zebrican embassy.

Heightening of tension over meeting Mkali

Discussion of the meaning of Hearthwarming

Vital discussion of the economics of Zebrica-Equestria trade relations

Dotted has plans for Hearthwarming

Scene 4: Dotted's office.

Dotted insists Leafy goes home for Hearthwarming

Dotted has plans for Hearthwarming

Scene 5: Dotted's office.

Dotted's plans for Hearthwarming are to work at his desk so everypony else can go home

Dotted is lonely and sad even though he won't admit it to himself

Scene 6: Celestia's study.

Celestia also missed Hearthwarming because she was doing Dotted's work for him just as he was doing that work for the other ponies

Dotted puts a blanket over her, takes the paperwork, and returns to his office, re-invigorated by the Princess' example, its proof of his importance to her, its vindication of his own actions, and his ability to be useful and repay her love

Nice Christmas colors, Bad Horse!

They are nice, aren't they?  They are about Christmas, because the story is about one meaning of Christmas.  But they're also color-coding the story.  Elements that address the story's theme are green.  Elements that grab the reader and string her along between the green bits are red.

Neither of us were able to think of a subplot introducing the theme that was short and funny enough to open with, so he came up with the Sandy Claws opener, which is funny, short, and doesn't set up any distracting expectations.  After that hook, almost everything in the story derives from the theme, which is told in scene 3, discussion of the meaning of Hearthwarming, and shown in scene 6.  GOH came up with a "plot" revolving around the Zebra ambassador because she, an outsider, can ask what the meaning of Hearthwarming is.  GOH threw out some earlier plots because they didn't directly contribute to the theme, and because they set up a conflict and an expectation for a confrontation with the antagonist and a resolution of that conflict, which would have derailed the story.  He changed Dotted's "meaning of Hearthwarming" explanation from what it was previously (more in line with standard Christmas theory) to what it is now so that it made his story's theme clear:

"I guess you could say it is about being thoughtful. A reminder to not only love, but to be mindful of that love, and to be grateful for having somepony to share it with."

The tension with Mkali  is just long enough to create some tension and drag the reader along, then be defused before the reader's forgotten about the true conflict driving the story, which was planted in scene 2:  Dotted wants to make sure everypony else gets home for Hearthswarming.  We immediately return to that in scene 4 with Leafy, and from there on it's all theme, all the time, until the clincher at the end, repeating the refrain Dotted has been repeating throughout the story, which was first optimistic, then tragic, and is now triumphant.

THIS IS WHY I LOVE THIS STORY.

Bonus meta-rant:  See, analyzing something doesn't ruin it by taking away the mystery!  It makes it better.