The short version is that standard, universal terms will work via an indirect reference (tell application x), but application-specific terms won't.

This includes standard commands such as 'open', 'close', 'quit', 'activate', plus a few standard object types. All applications should respond to these.

In this case, although you might think that miniaturized is standard, it isn't universal. Not all applications support this property for their windows, so it depends entirely on the application and therefore needs a specific 'tell' or 'using terms from...' (so that the Script Editor can understand which dictionary terms are available).