No, not quite. SPOILER should conceal text even when you're looking directly at the node in question - unlike READMORE which reveals the text at that point. You are right that for someone reading the front page or the section pages, or seeing a note in the context of a different node, READMORE does that job. However for those of us using Newest Nodes (or its ticker, in some form), that isn't very helpful, as you will then routinely be looking at nodes (and not only root nodes) directly.

Makeshifts last the longest.