Why wouldn’t he know it? It’s a famous song by a well known composer.
And he’s certainly aware of Gilbert & Sullivan.
I doubt whether he listens to Victorian drawing-room songs. (Lyrics by Adelaide Proctor, not Gilbert.)
There are a couple of well known G&S patter songs, but all the more serious songs, sad songs, beautiful songs from the Savoy operas are far less known today.
I’d love to see that with proper error propagation.
Ask at the talk page for the explain xkcd entry, and somebody there might be willing to tackle that for you.
There’s a step-by-step table on the explainxkcd wiki.
It really depends on what you mean by “proper error propagation”.
I’ll have to work it out myself. 
I’m thinking of something like the variance of the initial 17 mph is (\pm 0.5 mph)^2. Then the variance of the next step, 8 m/s is (\pm 0.5 mph)^2 + (\pm 0.5 m/s)^2. And so on…
Eliding the math…
| Value | Error | Length Unit | Time Unit | |
|---|---|---|---|---|
| 17.0 | 0.5 | mile | / | hour |
| 8.0 | 0.5 | meter | / | second |
| 16.0 | 1.2 | nautical mile | / | hour |
| 5.0 | 0.6 | fathom | / | second |
| 3.0 | 0.6 | furlong | / | minute |
| 6.0 | 1.2 | fathom | / | second |
| 40.0 | 7.9 | kilometer | / | hour |
| 22.0 | 4.3 | nautical mile | / | hour |
| 41.0 | 8.0 | kilometer | / | hour |
| 204.0 | 39.8 | furlong | / | hour |
| 26.0 | 5.0 | mile | / | hour |
| 12.0 | 2.3 | meter | / | second |
| 4.0 | 0.8 | furlong | / | minute |
| 15.0 | 3.1 | yard | / | second |
| 8.0 | 1.7 | fathom | / | second |
| 15.0 | 3.1 | meter | / | second |
| 34.0 | 6.9 | mile | / | hour |
| 5.0 | 1.0 | furlong | / | minute |
| 33.0 | 6.8 | nautical mile | / | hour |
| 19.0 | 3.9 | yard | / | second |
| 10.0 | 2.0 | fathom | / | second |
| 36.0 | 7.1 | nautical mile | / | hour |
| 6.0 | 1.2 | furlong | / | minute |
| 45.0 | 9.0 | mile | / | hour |
Hmm, it seems the error is not normal. 
I feel like I’ve already seen a very similar XKCD…
It felt familiar to me, too, but I couldn’t find one. He used to sell a T-shirt with all the different things that Greek letters could represent - maybe that’s what we’re thinking of? His store seems to be closed right now, though.
This one, right? Only last year:
Yup, that’s the one I was thinking of.
I once graded for a class, where one student liked to use Cyrillic letters for his auxiliary variables. OK, fine, you can use whatever you want for auxiliary variables, and it made it unlikely that he’d accidentally collide with any letters already in the problem… except that he liked to use both Ш and Щ, and it took me a while to realize those were two different letters.
Oh, and…
Really, they look nothing alike. ш and т, on the other hand…
(soon you wind up with http://i.imgur.com/DdSNkI3.jpg )
Some of us would create our own symbols. :evil:
I am totally down for a Sporcle geography tournament. I’m very good at “Countries of the World”. My personal best is 195 out of 197.