Whittling covers a broad range of work and can use an equally broad range of blades. My grandfather did a lot of woodwork with hand powered blades which included heavy stock removal tools like hatchets with broad curving faces and draw knives and of course a wide selection of blades for more precise work.
There was a wide variety of blade geometries being used here as the forces that each took varied a lot. The small carving blades were very thin, and very hard with very acute bevels. This is necessary to allow long lasting carving sessions which want a long lasting edge and a low rate of hand fatigue so you can be accurate and precise for a long time.
The heavy stock removal tools will be used with much more force so they need to be much more robust and they need to be able to handle twists as well as impacts off of knots etc. . Some purists will only use one tool, generally the heavy stock removal one like an axe. It will generally then be a lot finer at the edge that for someone who just uses it for heavy stock removal.
Anyway, all that being said, when most people use the term whittling, they are talking very low stress slicing into wood. Something that can be done for hours with no real effort or strain. Even a simple SAK can do that with no problems.
-Cliff
