To be clear:

There is a colossal difference between a chord progression and a melodic passage.

I can use the C-Am-F-G all day long in writing and not be infringing. On the other hand, if (over the same chord progression) I write a song with the same melody as Buddy Holly's "Everyday", I could (and should) get my butt sued.

Courts have erred, in the opinion of many, in applying too broad of an infringement brushstroke over chord progressions and "feels". Several such cases are under appeal and will probably be overturned (if common sense prevails).

Just a point of clarification to hopefully make apples to apples comparisons and conversations.

http://www.rogerbrownsongs.com
http://www.nashvillesongwriters.com/roger-brown