"Wouldn't a slower cable slow all parts of signal down, not just one part?"
In a nutshell, probably not. Signal propagation of all sorts, including that associated with a wire conducting an electrical signals, is highly frequency dependent in theory. It's just a matter of how much and whether significant enough to matter or not in any particular case. I believe it is significant enough to matter for many with discerning ears in the case of speaker cables. Even more so in the case of analog ICs. At least, that is my assessment based on my personal listening experiences.
In a nutshell, probably not. Signal propagation of all sorts, including that associated with a wire conducting an electrical signals, is highly frequency dependent in theory. It's just a matter of how much and whether significant enough to matter or not in any particular case. I believe it is significant enough to matter for many with discerning ears in the case of speaker cables. Even more so in the case of analog ICs. At least, that is my assessment based on my personal listening experiences.