You are correct. I am a Hindu and I also have seen several of my kind perform differently in religious observation. Easier way to understand this is to understand the hierarchy of implicit organization. The order goes as follows.
Religion - Offcourse Hindu (Some argue that Hinduism is way of living, Sanatana is religion).
Varna - Ex. Brahmin (Not Brahmana), Kshatriya, Vaishya and Shudra
Caste - Ex. Nair (from Kerala), Kayastha
Subcaste - Ex. Nambiyar (sub of Nair), Menon (sub of Nair), Mahur (Sub of Kayastha).
Regional / Community - Location or region of your residence
Family - Individual's family committments
Individual - Personal committments
How this works then ...
Every level above has set of rules, properties, characteristics and behaviors that are defined and followed.
Every level below inherits everything from level above.
Every level may define some new characteristics or behaviors that are not in it's parent level.
Every level may modify or override the characteristics, behaviors and rules from its parent and pass on to it's child level as it's own.
Over the time, familities living far from their place of origin have seen some infusion of local prevalent practices into their own.
Some families worship a perticular God or Goddess as tradition that changes certain rules.
Some individuals take up some vows that also result in individual's behaviors and practices.
Best way to describe this is via Software Concept of Object Orientation. Four basic principles of object orientation describes how this work. Every level follows the four principles.. Abstraction, Encapsulation, Inheritence and Polymorphism.
Ref : http://en.wikipedia.org/wiki/Object-oriented_programming