I believe it's to give a big invetive to land on the runway. Otherwise people will just ignore tham and put the plan down anywhere.
It annoys me sometimes too. Managed to get an La5 that was missing the outer half of the left wing all the way home, lined up on the runway, flaps and gear down. At this speed it's almost impossible to keep the wings level and I ended up missing the runway, bouncing around a bit and ripped the gear off. Exit within spitting distance of one of the hangers and I get a ditch =(
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Graywolfe <tim@flibble.org>