Weirdness with =?

I had this code in a script:

UPDATE food_foods SET included=true WHERE verification_status = 'I';
UPDATE food_foods SET included=false WHERE verification_status IS NULL;

I tried replacing it with:

UPDATE food_foods SET included=(verification_status = 'I');

However, that set included to true only where verification_status=I, it 
didn't set false at all.

Why doesn't this work?

Chris