Has anyone else noticed how odd these benchmarks seem? They run sunspider on different browsers in different OSes and use the results to compare processor perf

Has anyone else noticed how odd these benchmarks seem? They run sunspider on different browsers in different OSes and use the results to compare processor performance per watt. On the same OS, with the same browser, I can have higher variations on performance per watt with a single compiler flag (fastmath, -O2 vs -O3, etc). The same could be said by changing the kernel's scheduler. If we keep in mind that the browser, compiler and OS are all different for these tests, how can we accept the results as anything but noise from those differences? One striking example of this is that the new version of chrome on the nexus 10 could easily account for the performance difference in the kraken test. How can we use that data to compare the performance per watt of the processors?