Drunken Wolf,
It's not just a matter of bandwidth, but rather the number and complexity of processing steps. Component video, which is analog, is only limited by the bandwidth of the amplifier used to drive the cable and the receiving OP-Amps to convert it to whatever is necessary - 720p or 1080i.
Most OP-Amps today can easily handle over 100 MHz of bandwidth. But HD signals, either 720p or 1080i, require only 35 MHz of bandwidth; 1080p requires 65MHz of bandwidth, so all of these are easily accommodated by component video connections. The real issue is what happens to the data once it's received. In the case of component video (it's an analog signal), it is processed by the ADCs (analog to digital converters) and sent directly to the display device.
But in the case of HDMI connection, the data must be sent to another chip set (no ADCs needed because it's a digital connection), which then has to strip out the video information, then decide what to do with it. A different chip set deals with the anti-piracy handshake process. This processing can have bit jitter, clocking issues, missed or corrupted bits, etc. It's still a contentious subject in "Pure Digital" video systems.
All of this is bypassed with component video connection, where the audio is routed with separate cables.
Using HDMI, there are up to five different digital chip sets involved in separating the video, the piracy codes, and the digital audio stream.
There are issues in digital audio as well when the clock changes or bit stream changes from one Dolby Digital system to another or from PCM to Dolby Digital. And the processing of the audio stream is relatively simple compared to the video stream.
So the bottom line is that there are just too many digital processing steps with HDMI connection.
