While it might be helpful to know some HTML, most of the time, an embedded developer (just as an example) will not need that knowledge, not hone it and, as a result, not be able to use it either way. It's the same for other types of software engineers. There are some rather theoretical architects, there are low-level developers (OS, drivers, etc.), there are desktop application developers and last but not least specialized app developers. Web dev is a nice-to-have, but should they know it? I don't think so and I would never require them to.