I've seen falcons in the suburbs where both my brother and mother live, in Orange and San Jose CA. Both of these subdivisions were built before DDT was banned, but there weren't any falcons there until recently.
That falcons do well among skyscrapers is a given. But I've seen falcons roost in skyscrapers that had no special provision for them.
Since skyscrapers and subdivisions existed when falcon populations were in decline, the population of the falcons since then in both urban and suburban envirionments can't be attributed exclusively to habitat preservation or special building provisions.
So, if not them, and not the DDT ban, then what is responsible for the falcons' comeback?