[MDL ED] Multiple Materials - Single Object

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That and also using several small tileable textures on the same object...Which is generally good for performance if you have a lot of objects using the same textures, but it doesn't work for an infinite number of textures per object if you know what I mean.
At some point the drawcalls required to look up several textures for one object can be worse for performance than having a few more textures lying around in memory. Maybe hpl is especially sensitive when it comes to that and that's why they used unique textures? Another reason might be that they wanted unique, baked normal maps for the objects and HPL doesn't support different uv channels for different maps.