That's what I thought as well. I than realized that the Uncharted 2 Tone Mapper operates on the individual color channels as well as my tone mapping operator. I fixed my tone mapping operator implementation after realizing that it might be better to tonemap the luminance instead. But it turned out, that the resulting image looked sooo much worse, that I immediately switched back to the old implementation. Just look at Hable's blog entry. All of his tone mapping operator implementations operate on the individual color channels as well. And when you think about it, the cones on the human retina independently convert the light into nerve impulses. That's why I think it actually makes sense to perform it on a per channel basis.
5. Prevent saturation of single channels to avoid a color shift (=> tone mapper)
Also, just take a look at this bright light:
The color shifts to white in the center. This has nothing to do with the white point. It's actually a color shift.