I guess we do treat them differently - but that is because they are different.
Girls are independent from an early age, and puberty commences a fractious relationship with their mothers because mothers see all their faults writ large in their teenage daughters, and what will make them close as adults can make them fight as adult and teenager.
Girls are often close to their fathers because they mirror the character facets that makes their dad love their mum.
Boys usually develop a close bond with their mothers, which continues without interuption into adulthood, so an element of that natural protectiveness that any mother has for any child of either gender, continues.
Boys can often have fractious relationships as they develop into adulthood because some men do not adapt well to another 'male' in the house - but these are generalisations, and I appreciate that.
So yes, we do treat them differently, but that is the way nature made us - and them.