In reply to nickcj:
> The more metal in contact with rock, the more holding power. So grooves not always necessarily add more grip...
Probably not true for all rock types and placements.
The science and understanding of micro and macro friction are very complex and probably incomplete.
Any cam design is a compromise for varying rock types and placements.
A cynical view is that they are probably just designed to look "right" and maximise sales
Though since the OP asked the question possibly not.