I think it’s because, although slow, they are mighty and win the race through persistence and consistency. They can also be represented with old-school emoticons.

So the ongoing joke I have with @orthwyrm is that if he doesn’t post it’s either because he forgot or the price has gone to 100k and no one told me. We used to race each other to post first in the old Daily Discussion thread and my posts were (and are) my way of encouraging / goading him. No chance of getting in first these days though!