Pg intentionally does not do any casting, as it is a binding to libpq. We're working on a mixin that would allow you to add typecasting, which will include Boolean fields, but until then if you want typecasting use a library like Sequel or DataMapper.
ActiveRecord is a third API that provides typecasting.
Well, no one asked for it, but I felt like giving my opinion to the topic: Even if the typecasting feature is something that is requested from time to time, I consider the current API as the best way to go. Data type conversions are never 100% settled, as Jeff Davis sad and can be context dependent. Therefore I would leave it to the higher levels to do type conversions.