I was intrigued that Mike considered the Spotmatic SL to be a "loss leader" when it was released in about 1968. It might be good to consider that the SV left the market about the same time with the SL filling its slot. It would require some research, but I suspect that the price points for both the SV and SL were not that far off that of the SP. While TTL metering has its advantages, my memory is that many serious photographers preferred to continue use of their hand-held meters such that a camera such as the SL would not be without its fans. Note too that it was 23 grams lighter than the SP.
Steve
(...also thought it strange that he thinks the MX replaced the Spotmatic...KM perhaps?)