Note that my interpretation of the rules is that the centre dot should be used for clarification for Ski-O controls where it is required, not necessarily for the whole course.
The newer 2010 MTB rules makes this very clear by having 2 different symbols, the dotted circle for where it is needed and the empty one for other places (702 and 840).
I am a bit puzzled why the Ski-O one is 810 - maybe there is a different range of circle dimensions for the two. There is a slight variation in size of centre dot I suppose. The other difference is nasty - when layering colours the Purple circle should be below the Green colour used for the Ski-O tracks, but the centre-dot has to be ABOVE the Green so it can be seen ... I don't know about MTB-O w.r.t this.
I guess ideally I'd like to see all courses have a default circle of no-dot with the option to change on a per-control basis (an additional per-course default might also be appropriate). I include Foot-O in this only since for some types of lower-key micro-sprints I have used centre-dot in the past so I didn't need to provide control descriptions.
Apart from the centre-dot are there any other differences between Ski-O and Foot-O in CONDES? Availability of equipment change for instance?
Cheers
JK