I could be mistaken on that point. However (here it comes), there is just something about the images I take with a wide on a croped camera that feels amis. Something about it just doesn't feel as natural as images I've taken and seen from full-frame sensors (or film). Can't put my finger on it exactly.
Without a full-frame D-SLR to compare to I can't narrow it down. The perspective distortion thing seemed the most logical.
Yes, I think you are.
That's a paralax issue with the viewfinder. The image is in fact cropped. The full image come from the image circle the lens is designed to create. The smaller sensor only captures the very center crop of that.
No, this has nothing to do with parallax, just that the viewfinder does not see 100% of the image cast on the sensor with the 20D.