Simplifying to Get Down an Idea

I found another deal at the bookstore a few weeks ago. I found this book of drawings for $5. It's a great big huge book with lots of drawings, both by names you would recognize and some from names you wouldn't.

I was looking at some of the sketches, where the artist was working out ideas, composition and layout. I was amazed at their short hand for faces - you can get alot of structure with just a few triangles. Above you see some of the copies I made, after Rubens and Rembrandt. They are just simple shapes put in to stand for features. Of course, that idea doesn't sound revolutionary, but when I go to sketch out an idea, I end up using lines, not shapes. Perhaps this is why I draw and not paint. It sort of clicked in my mind with some things I have reading, more on that later.