That means registered Wii developers now have access to the PhysX software development toolkit. It doesn't look like they're getting the kit for free, though: the official press release says the Wii SDK is "available for license directly from NVIDIA." Nvidia's official PhysX page still doesn't mention the Wii, but it says licensing the PhysX source code for the PC and Xbox 360 costs $50,000 per application.
Since the Wii lacks a fancy multi-core CPU like the PS3 and Xbox 360—or a DirectX 10-class programmable GPU like Nvidia's current graphics cards, for that matter—the PhysX toolkit's "robust physics engine" likely runs in a less potent form on the Wii. You probably shouldn't expect fancy fluid dynamic effects and cloth simulations, then, especially considering the spartan nature of the Wii's hardware.