It seems to me that many people, not just Indians, do not use the pronoun whom very often, if at all; maybe they do not know when to use it, so they just stick to who.
In order to get an idea of how widespread this practice is, I googled "who did he talk to" and got 599,ooo results. Then I searched the grammatically correct version of that sentence, "whom did he talk to", and got a mere 49,000 results!
I performed another search and the results were equally revealing. This time I entered "who do you think you are talking to" and it's grammatically correct sibling "whom do you think ..."; the results for the former were many times greater than for the latter.
But it's not difficult to understand if you put in a little effort. Let me explain.
Who and whom are used just like he and him. All four of these words are pronouns; who and he are known as 'subject pronouns' while 'whom' and 'him' are 'object pronouns'. The subject of a sentence is a noun or a pronoun which performs an action and the object is the recipient.
Let's take an example. Let's suppose that a female teacher scolded one of her male students. Using pronouns we can say:
"She scolded him." The female teacher was the one who performed the action, so she is the subject and is represented by the subject pronoun she, and the student is represented by the object pronoun him.
If you don't know who the recipient of the action was then you can ask the question "Whom did she scold?" using the object pronoun whom. Here, who would have been wrong since it can represent only the subject of a sentence, which in our example is the teacher.
Let's take the first sentence that I googled, "who did he talk to". Imagine yourself answering that question with "he talked to ____". Here, he is the subject since he is the one performing the action of talking. So the pronoun to fill the blank will have to be the object pronoun whom, not the subject pronoun who.
Similarly, if you were to answer the second sentence, "who do you think you are talking to", you would say "I am talking to _____". Here again, I is performing the action and is therefore the subject and the recipient of the action, and the object, needs to be represented by the object pronoun whom.
I hope I haven't confused you further. More lucid explanations can be found here and here.