That is correct. You don't buy a seat. You buy access to that flight so to speak. People are very possessive about their seat, thinking they are purchasing that particular seat. We would all get along and sing songs while holding hands, if delta would stop changing aircraft and swapping seat assignments and us glaring at the person sitting in "our seat" on our way to our newly assigned seat. Lol we have all done the quick glance at our former seat to see if they belong there.