Since the full volume of oil going to the bearings does not have to pass through the filter, the pores of the element can be tighter. Most bypass filters actually do a better job of filtering than a full flow, they just don't filter all the oil at once.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!