Why is the TDS7254/B not recommended for more than XGA resolution?

Why is the TDS7254/B not recommended for more than XGA resolution?

TDS7254/B Oscilloscopes typical rise time is 83ps for 20% to 80% signal rise time. As a rule of thumb, the Oscilloscope rise time should be at least 3 to 4 times faster than the signal rise time. For XGA resolution the compliance test specification rise time limit is around 400ps, but the designs will be around 200ps to 300ps. This is with in the range of TDS7254/B Oscilloscope. For the higher resolutions the signals rise time will be less than 200ps, so it is not recommended to use TDS7254/B Oscilloscopes.