...because it is more powerful.

Unity has a very sophisticated lightmapper, they integrated a professional tool that has been used for games like Mirrors Edge as an example. It renders not only simple lighting, but also radiosity and ambient occlusion. It can use HDR image as light source. I can even do the entire lighting only from textures, where a texture contains light emission channels. For instance some of my sci-fi textures have lights painted in and I have additional glow maps make them bright even when no light is around. These glow maps can be the source to calculate the lightmaps and create amazing soft lighting.

Besides that you can combine shaders and dynamic lights with your lightmaps.

There are way more examples. You can believe me, this technology is far behind the WED lightmapper. Also there will be directional lightmapping in the next release, similar to UDK, Source and Vision. This means that normal and spec mapping will read the lighting directions from the static lightmaps and will be more realistic when moving around.

Also some light probes will be in the next edition that allow to influence moving objects by the static lightmaps. So even a flying object gets correct light, color and lighting direction without a trace to the ground, just by moving through a volume with lighting information attached.