Indeed.
However filters also act as a significant impediment to air flow especially when then get clogged up, and because of that designers often prefer to design gravity traps along the air flow path as a more attractive alternative.
As far as what I have seen, dust seems to be the biggest problem particularly for those of us you drive with the windows down in dusty environments. If you drive with the windows up chances are the IPU will be relatively clean even after 5 years or more.
Cheers;
MSantos