I've never had a friction shifting setup where I felt the upshift to be as smooth as the downshift... To go to the small ring you're literally knocking off and dropping the chain in front while simultaneously releasing tension on the rear derailleur spring lower spring. To upshift you're forcefully pushing the chain up into position with the the front derailleur cage and creating tension on the rear derailleur when the chain tightens up. I can't imagine how out why it should be as smooth in the one direction as the other. Maybe that's a poor assumption, though!
-Gregory