Clash of Cultures- The yearning to pay!

I go out with friends. Who pays? Why is it such an issue with some people?
I go out with a group of friends, split the bill, awesome. Works brilliant. Or we all buy something, and share. That works too.
Then there are the times you go with just antoher person, where its easier for just one person to pay. The complicated times. Maybe I should never go on such occassions, but then these are the best times you get to know another person. Anyways, it would make sense to take turns at such occassions to pay. If you pay once, the next time, they should let you pay. Why do some people always insist they pay? and then use useless excuses that I'm a girl, they feel insulted, etc. I mean, come on, what abt my feelings and my worries that they may insult girls for never taking out their wallet? Why don't people let me pay sometimes?
I ask this having full well witnessed some of the worst fights back in India, of who pays after a lunch or dinner, especialy when you take extended family out to a restaurant. I supppose its associated with being Indian. Cos it works really well when I go to lunch/dinner with Aussie friends. I mean, even at a Bday dinner, there is not concept of 'treat' and everyone pays for themself. At a wedding, people are expected to give gifts that match the costs of the wedding per person. Although, I could never understand these concepts, nor agree with it; what happened to the moderate middle ground, where when you go on a normal day out, that you can pay sometimes. Special days, the pay is yours, no worries:)!