Do all Hindus need a GURU?
The answer is NO. NO. NO.
Do all Hindus have a Guru?
The overwhelming majority of the Hindus do not have a Guru. Even among the small minority of the people who claim to have a Guru most of them do not have a Guru as defined in the scriptures.
Definition of the term Guru:
Based on a long line of philosophical understanding as to the importance of knowledge, the guru is seen as a sacred conduit, or a way to self-realization. In India and among people of Hindu, Buddhist, or Sikh belief, the title retains a hallowed meaning.
Kula Guru: The Guru of a clan or tribe. Sukracharya was the Guru of the Asuras. Brahaspathi was the Guru of the Devas.
Raja Guru: The Guru of the King.
These are the only terms used in the Puranas. Only individuals who were seeking a way to self-realization had a Guru. Such seekers were called disciples.
The Bhakthi and Guru (Social Reform) Movements:
The Bhakthi movement started around 700 A.D in Tamil Nadu with the Nayanmars. It spread later all over India. The basic principles of the Bhakthi movement was the break from Rituals and the Varnashrama system. Later on this movement resulted in many Guru mevements.
Some of the major ones are:
Nath/Siddhas: Matsyendra Nath (Maccha Muni in Tamil), Gorakshak Nath/Gorak Nath (Gorakkar in Tamil), Thirumular and others.
Guru Nanak and his disciples: Which later on became a seperate religion. This movement included some of the teachings of the earlier Saints like Kabhir and the Nath/Siddhas.
These are called social reform movements because they were founded by non-Brhmins and were against the Rituals and Varnashrama Dharma.
These movements placed a lot of emphasis on the Guru. The Guru became the leader of the movement. More like a Kula Guru than the original concept of a Guru. All those who followed these Saints took them as their Guru. Of course this intepretation of a Guru originated in the concept of a Gotra or a clan which followed cerain Pravara Rishis or Gurus.