You make an interesting point Buster. It makes you wonder what sort of angle the slide would be if the right main gear collapsed.
And here is the interesting question. Excluding the 737, why do we insist on disarming the slides and opening the doors ourselves? What is the benefit? Virtually all aircraft will self-disarm the slides if the doors or opened from the outside. By allowing ground crews to open doors you reduce the possibility of finger trouble but more importantly, reduce cabin crews' door opening repertoire to 'in emergency only'. The benefit of that is when push comes to shove, a disarmed door won't be opened in error. It speaks volumes for cabin crew that this has rarely happened but emergencies they need all the help we can give them.