ASP.Net is a great example of this. Employers think (if they're aware of it) that the API is all you need to know along with the language, for a particular kind of application. The standard API becomes a part of the "design language" for the project. The problem is the API, not to mention the development tool you're using, can steer you into all sorts of really bad design decisions. Nevertheless the expectation is you'll use the dev. tool and API, because it's just faster to go along with what it demands, because it carries all this functionality you need inside it. The problem is it can create a bug-ridden nightmare of a design, which slows you down in the acceptance test phase, not to mention maintenance. The path of better design would demand that you use the features of the dev. tool, and API, less, and design your own class library, even if it's small, despite the fact that it could take you longer to complete the implementation (code generation, anyone?)