Yes, they are common names because they are all native religions. Hinduism is just a name that is given to the common culture/believes/value system that exists all across India. It is a relatively new name as well. Hundreds of years ago, this term was not even known. Sikhism, Buddhism, Jainism all came from within Hinduism. They all made certain changes to the native religion so as to "reform" the social practises. That is why they share so much with other Hindus. That is why the constitution of India includes references to Hindu to include all other native religions. We share as much of the commonalities with Hinduism as brahmins, gujars, yadavas, dalits, etc. As for differences, all castes have their own unique customs and traditions. You want to have Hindu names, pray to Hindu gods, have Hindu scriptures and yet call yourself as non-Hindu! There is always a constituency for weird ideas, but don't expect it to fly with many.