Backhanded compliments, Entertainment Weekly style

Entertainment Weekly lists the 10 funniest movie dads of all time. Maybe, due to the grades handed out, it should have offered a Top 5:

Jim's Dad (Eugene Levy), "American Pie" - EW Grade: B
Henry Jones Sr. (Sean Connery), "Indiana Jones and the Last Crusade" - EW Grade: A
Armand & Albert Goldman (Robin Williams, Nathan Lane), "The Birdcage" - EW Grade: A-
Clark Griswold (Chevy Chase), "National Lampoon's Vacation" - EW Grade: C
Sonny Koufax (Adam Sandler), "Big Daddy" - EW Grade: B-
Royal Tenenbaum (Gene Hackman), "The Royal Tenenbaums" - EW Grade: A
Sheldon Kornpett & Vince Ricardo (Alan Arkin, Peter Falk), "The In-Laws" - EW Grade: N/A
Gil Buckman (Steve Martin), "Parenthood" - EW Grade: A-
Old Man Dunphy (Alec Baldwin), "Outside Providence" - EW Grade: C-
Bernie Focker (Dustin Hoffman), "Meet the Fockers" - EW Grade: B-

Three questions to ask:

1. How did "National Lampoon's Vacation" get an underwhelming C?
2. How did "Meet The Fockers" get an overwhelming B-?
3. How did the original "The In-Laws," evidently worthy of making this list, not merit an EW grade? (And I don't wanna hear, "Oh, Entertainment Weekly wasn't around back in 1979." It wasn't around for "National Lampoon's Vacation," either, and that classic somehow got a ridiculous C rating.)