Small Meta: On the Use of Names in Pairings

Not really meta, as such. Just an interesting series of observations I blundered through while considering the following:

Holmes/Watson vs John/Mary (Downey filmes)
Vimes/Vetinari vs Sam/Sybil (Discworld)

The names, I mean, not the pairings themselves.

I was just thinking about this in terms of my having written Sybil/Sam/Havelock and Sherlock/John/Mary. Just noticing the choice of names used for each pairing tag. I noticed it even at the time, when I was putting the threesomes in the headers for the fics and noticed the odd ... stickiness of the names? Just taking those two. The Discworld set, do you say Vimes/Vetinari/Sybil? Vimes/Vetinari/Ramkin? Sam/Sybil/Havelock? With the Holmes set, is it Holmes/Watson/Mary, or Holmes/Watson/Morstan, or Sherlock/John/Mary?

None of them really look right, laid out. And there are a couple of reasons for that, and also a couple of implications, and right now I'm sort of randomly finding this fascinating. Heh. So. Bear with me while I unpick it a little?

( On the Use of Names in Pairings )