If the third-party thumbnailer is implemented as a shared library (DLL) that Explorer is configured to load, then sure, a segfault or similar in the library will kill the whole process. Not sure how that's Microsoft's fault. Sure, there's an argument that loading a library is the wrong model, but there's a performance tradeoff, especially given Windows' relatively slow IPC capabilities. The real surprise here is that Linux manages to be comparably slow, but when you complicate a simple, fast IPC model with dbus and a million other middleware layers, I suppose it starts to make more sense.