The explanation I understood was that invalid expressions like “Finder” evaluated to an odd number. Since jumping to an odd address is disallowed on the older 68K machines, the default failure behavior was to exit the current application. People used to claim that the code above was more reliable, but maybe this was superstitious: in practice everything is unreliable once you’ve encountered a serious bug on a system without memory protection.
ETA: I wonder if anyone else still has that burned into their brains and knows what I’m talking about. Maybe I’m crazy.