In this case, he's working with external code (Intel's example code) that happened to use data in that way. Why - good question. I guess someone at Intel though

In this case, he's working with external code (Intel's example code) that happened to use data in that way. Why - good question. I guess someone at Intel thought "hey this is just example code how to do software rasterizer for occlusion, who cares what is the data format" and went with that. Badly ;)