DIRECTV’s television signals are compressed digital signals. The DIRECTV/TiVo units are equipped with technology that allows the TiVo to record those compressed digital signals directly to the TiVo’s hard drive. Therefore, when the signal is recorded and then played back through the TiVo, there is no quality loss. Thus, the DIRECTV/TiVo units record in only one quality: Best.
On the other hand, the Standalone TiVo units (which work with cable and satellite) convert the signal into digital form. At the time of this conversion, the TiVo must compress the signal prior to saving it to the hard drive. This is true even if the Standalone TiVo is connected to a DIRECTV receiver or a digital cable box.