Not for employees that take their annual leave on those days! It's no more a working day *for them* as a bank holiday.
Otherwise using that logic, my employer has 365 working days per year!
They're both benefits which have a value, and a fixed value regardless of what overtime you do. Ie your overtime rate should really include the value of your pension, health insurance, sick pay "insurance" etc added to your annual salary..a bit like bank holidays and annual leave.
Yes, it's usually at the discretion of the employer.
Still more than the normal hourly rate. There again, when you include pension benefits etc....