I'm used to it, so I didn't think about it like that. You're right...
But on the other hand... postgresql strictly follows SQL standards with logical operators AND, OR, NOT. Duplicating it if for me confusing and unnecessary. I personally would never use || in place of logical OR in SQL - simple because it's "less visible"... I like to write all SQL key words in capitals and attributes and everything else in small letters - so it's for me easier to read and understand the semantics.
Cheers!
Btw. the expression OR 'string_constant' doesn't evaluate to TRUE either. It triggers type error in pgsql - "invalid input syntax for type boolean"