Sausage,

you are intrinsically correct when you say a chord progression is simply a succession of chords. But, deciding exactly which chords is the key to giving a song that special touch, a certain "character", a unique sound, etc.

Those websites will show you how to make those chords...but they donlt tell you how to put them together to create a certain sound or character. you could know a thousand chords...but if you had no idea how to use them they are considerably less valuable to you.

as an example, to go from C to F, a simple progression...or not!!! you could just go C-C7-F. That is often a good enough progression. However, you could also go C-Am7-C7-F, or C-Aflat-C7sus4-C7/Aflat-F, or C-Em-Am7-C7-F, or C-Caug-F, etc. There are many other ways to make that one progression. And each one gives the song a different color or character.

A goos example of how one chord progression can be a memorable part of a song is Willie Nelson's "Blue Eyes Crying In The Rain". The chord progression he uses to go from E to A as he goes into the chorus is memorable because it is not standard but very pretty and gives the song a unique character.

So, yes, for composers, it is a big deal...a very big deal.

Hope that helped tp answer at least part of your question.

Alan