Is camo a "must" ? Maybe...Maybe not...but...
I personally wear camo clothing (any pattern) because most manufacturers will make/sell an excellent quality product (ie. Goretex, Thinsulate, quieter materials, light weight, extra pockets, etc, etc) for your comfort and flexibility. Hard to find other type clothing with all these advantages. Just happens that most come in camo patterns.
So I guess the main reason why I wear same is I really like to stay warm and dry, making things more enjoyable in the bush.
As most know, being smart, still, quiet, patient, environmental trends, knowledge of the game you hunt, and so forth are probably better factors in being successful.