I'll check my 7s meter's coupling range when I get home tonight, but I'm guessing that Gandy is right. I've found typos on the Canon museum site before (mostly in lens weights.)
Having owned a 7, and currently owning the selenium meter for the VI/P series (which is actually more sensitive than the 7 model's built-in selenium meter) I can confirm that the 7s meter is more usable in low light. A selenium meter can certainly be just as accurate photometrically as a CdS meter, within its limitations -- but since the cell's output is lower in low-light conditions, the low end of the meter scale has to be more crowded together, making it more difficult to read out fractional f/stops.
If you're interested in doing really low-light photography, though, also note that even the 7s has a film speed scale that only goes to 400. This is a bit inconvenient for use with the faster films you'd normally choose under low light. Yes, you can take a reading and then compensate in your head -- but if you've got to do that extra work, you might almost as well be using a hand-held meter in the first place.