I'm an electrical engineer, and I've never been asked to design something from scratch in an interview. I have been shown existing design drawings or products and asked questions about them, which leads to various discussions. What we do in interviews is talk, both about what the company works on and about what I've worked on.
In any given specialty, I think good developers will pick up the stuff around that specialty. Java devs will learn about Maven and git and maybe some JVM customizations to tweak memory usage. Rails devs will learn about which gems are widely-used to solve specific problems, and git, and maybe some devops/deployment stuff with SSH keys and Capistrano.
The particulars matter less than that there's some amount of holistic knowledge of their specialty. Of course one can argue the specifics (what if they've used svn but never touched git, etc)... but if there are no specifics -- if the candidate only knows their specific language of choice but nothing outside of it -- I would argue that they're probably not that great.
And just to be constructive: you have a nugget of a good idea, that a technologist should have fairly detailed knowledge in some domain of interest. Finding what those areas are and getting them to speak about it beyond a superficial level of detail might be a good hiring criteria.