Looking at these tests, many of them still doesn't list any optimization flags, meaning they could very well be done with -O0 or -O1, thus making them totally pointless for a compiler optimization benchmark.
If we look at those few where we see the optimization flag listed (-O3), the results we often get a nice performance increase with the later GCC's, look at FFTE, C-Ray, POV-Ray, but the vast majority of the tests doesn't have any optimization flags listed and as such we don't know if those benchmarks are of any consequence whatsoever in terms of compiler optimization.
Then of course we have x264 and VP8, codebases which rely heavily on finely optimized assembly code for the performance critical parts, unless you explicitly disable the assembly code when configuring, these tests are totally worthless in terms of comparing compiler optimization. It's even more sad given that comparing how the compilers optimize this code would actually be very interesting results.
Now, given that -O0 is the default for GCC, unless we actually set a -On optimization level the tests will be done with no optimization, thus rendering them useless. So when Michael omits reporting any compiler optimization flags it's simply impossible to tell if the benchmarks have any value whatsoever.