The jets on the back of the locomotive are what make it for me.
I used to play with that toy as a kid. I distinctly remember an uncle asking why that train had rocket engines on the back. I was baffled. Why WOULDN'T a train have rocket engines on the back; they're awesome! The question simply didn't compute to my seven year old self.
Bringing this back around, I think the symbol of chaining APPs as a train with rocket engines, that can only hurtle over the finish line or derail horribly, is pretty appropriate.