I say fragile because if the app developer updates their app to use different calls, libraries, or system services on the native platform it will probably no longer work with WINE until an updated set of shims and adapters is built. This makes their adaptation, which is not emulation (as the WINE name asserts), very application specific and (in my opinion) very fragile. Basically WINE is installing software shims and adapters to replace only the native operating system dependent calls, libraries, and services that the specific application actually uses with ones that work similarly on the non-native platform. WINE is focused on getting individual apps running across platforms.
WINE/Crossover is targeting a different set of use cases than Parallels and VMWare.
