Wouldn't you agree that most programmers will have to use databases and should at least have a basic working knowledge of how they work?
Database specialists usually end up with very specific knowledge of a particular platform, for example Oracle where there are endless ways to tweak for performance, or replication or whatever. Modeling with RDBMS is usually very straightforward and ends up being only a minuscule fraction of what you do day to day.
programmers? While I hate the word I would agree some basic working knowledge is necessary. But if you post a job description looking for a php programmer, and then you bring people in and start asking questions about schema design where even a correct answer isn't correct because now you also want your programmer to be a software designer who does requirements gathering as well it's your own fault for expecting to be interviewing architects instead of programmers.
If you are looking for someone to do schema design, that damn well better be in the job description given to candidates before they apply, and your software engineers damn well better be compensated for the extra required skill.
Database specialists usually end up with very specific knowledge of a particular platform, for example Oracle where there are endless ways to tweak for performance, or replication or whatever. Modeling with RDBMS is usually very straightforward and ends up being only a minuscule fraction of what you do day to day.