[Ichthypresbyter]

This is why Sikhs are supposed to all have the same surname (Singh for men, Kaur for women). Sikhism has always been strongly opposed to the caste system- see, for instance, their tradition of offering free food to anyone who wants it as long as they will eat with everyone else there.

According to a Sikh friend, in practice, Sikhs are still aware of caste- in fact, Sikhs from a high-caste background are more likely to keep their family's original surname and add Singh/Kaur as a middle name.

[Igelau]

That might explain some things... I had an Indian colleague once who used to tell "Sikh jokes" that he claimed were his cultural equivalent of "Blond jokes".

[srean]

They are closer to the "An Irishman and a Scotsman …" genre. Part of the reason there are so many Sardar jokes (that's what they are called) is that they (the Sardars) are very sporting and secure people. They don't mind being a butt of these jokes and start many of those themselves. My roommate (who was a Sardar, equivalently, a Sikh) used to say he would keep two glasses, one filled with water and another empty, in the night on his bedstead because in the middle of the night he might be thirsty, but then he might not be. Things like these are essentially baits to encourage such jokes.

But back to the PP a big part of Sikhism's break from Hinduism was the rejection of casteism. So it is built in. Someone who is more familiar will be able to elaborate more. What I have heard is that its root lies in agrarian anti-caste movements.