I would say that people who sign up for Pinboard (+ pay ~$10) are much more likely to support a service that they like and rely on. Otherwise they would've chosen a free service like Diigo or Delicious to begin with.
English is not my first language, so I'm not sure. Does "makes $200K every year" mean net profit or just the income from which hosting still has to be subtracted from? If it's the latter, that means a lot more people are paying for archive.