I have a hard time understanding this.

Manufacturers don't do stuff that costs money, if they don't have to.

So, because the flame trap costs money to design and produce and because the parts associated with the flame trap cost money to design and produce, I've got to believe that there was a good reason for designing the flame trap in the first place.

Even the name says that it is important. "Flame Trap?" Does it sound like the function of this component is to trap a flame? A flame? What would a flame be doing there, in the intake system?

So, apparently, sometime in the development of the N/A engine, some Volvo engineer saw the possibility of a flame in the intake, or the engine crankcase.

I would think, what they most probably saw, was an incident where the engine backfired, sending a flame through the throttle body. At that point, without the flame trap, that flame could enter the engine's crankcase and, if that crankcase was filed with volatile vapors, the engine would become a large grenade.

Now, what is the motivation for Volvo, and it's dealers, for tossing the flame trap?

Maybe, in real-life, Volvo has not seen the 850 grenade scenario materialize, but they have seen untold numbers of 850s in the shop for blown rear main seals caused by plugged flame traps. Rather than risk the wrath of customers over rear main seal issues, they've decided to risk the grenade scenario.

But the bottom line is that the flame trap/rear main seal issue is only an issue if you never maintain your flame trap. If, however, at every other oil change, you clean your flame trap, you get the best of both worlds: a safe rear main seal and a disabled 5-cylinder grenade.