As an aside some people (Joey Adams IIRC, maybe others) have suggested that postgresql-simple should change the conversions so that ByteString represents postgresql's binary blobs, and not postgresql's text. (And get rid of the Binary type in the process)
This seems a perfectly reasonable suggestion to me, though I'm not particularly inclined to change the API either. If you'd like to adopt this suggestion, be my guest.
I don't think that API compatibility between the *-simples should be high priority; do whatever you think is best for sqlite-simple. Then hopefully in a few years we'll have some well-developed database-specific interfaces that can inform a next-generation HDBC interface.
Best,