The advantage of VR in-lens is that the image is stabilized for both the image sensor and the AF sensors, which sit up in the top of the viewfinder. In-camera stabilizers don't stabilize the image in the viewfinder, or for the AF system.
For shooting birds in flight at very high magnification, you need a very fast shutter, so fast camera shake isn't so much an issue. But if you can't keep the AF sensor over the target, it won't matter, because AF won't be able to track the bird. VR is a huge help for this, maybe a bigger help than in stabilizing the image.
This explains why the systems used extensively by pros (Nikon & Canon) stabilize in-lens, even if it's not the most economic method from the point of view of the consumer. In-camera stabilization is really a gimmick feature for consumer-level cameras. At this time, it's not the right way to do it, although that may change in the future of electronic viewfinders and fast contrast-detect AF systems that use sensor data instead of traditional AF systems.