Developers of embedded (real-time) systems can choose from a variety of operating systems. While some embedded operating systems provide very flexible APIs, e.g., a POSIX-compliant interface for run-time management, others have a completely static structure, which is generated at compile time by utilizing detailed application knowledge. A prominent example for the latter class from the domain of automotive operating systems is OSEK/OS and its successor AUTOSAR/OS. As we have shown in previous work, the design of the operating system has a strong impact on its vulnerability for system failure caused by hardware faults. This observation is gaining importance, because there is an ongoing trend towards low-power and low-cost, yet less reliable, hardware. This work quantifies the difference in vulnerability for soft errors in main memory of a flexible (dynamic) operating systems (eCos) and a static system (CiAO), which has an OSEK-compliant structure. We also analyze the additional degree of robustness that is achieved by hardening an operating system with software-based and hardware-based fault-tolerance measures and the corresponding costs. Covering this design space gives developers a better chance for good design decisions with respect to the trade-off between fault tolerance, resource consumption, and interface convenience. Our results indicate that with a combination of hardware- and software-based fault-tolerance measures, silent data corruptions in both operating systems can be reduced to below one percent (compared to eCos). However, the analyzed fault-tolerance mechanisms are expensive for the dynamic system, whereas the statically designed operating system can be hardened at much lower price.