IMO, both high resolutions and low resolutions are important. Low resolutions take the bottleneck off the GPU and place it on the CPU, so it highlights the real performance difference between CPUs. However, higher resolution place the bottleneck back on the GPU, and show what real world usage will be like.
Considering 1680x1050 is the second most common resolution on monitors today, it certainly is important that it is included in benchmarks, it gives people with these monitors an idea of what performance they can expect, and actually it is people with these "lower" resolutions that will see the most noticeable difference between CPUs. Oh, and just FYI, 1280x1024 is the 3rd most common monitor resolution, so that too is important in benchmarks as well, and again they will show a larger difference between CPUs than a higher resolution would.