Wow, what a turn this thread took.
Just for the record, U2 were meant to tour India in 1983. The War Tour was going to end with a leg through India, Japan, Australia, and New Zealand, but the band were exhausted after the gruelling schedule through Europe and North America and only did the Japanese dates. Australia and New Zealand were pushed back to the start of the UF Tour - which had a very War-esque setlist - but India never happened. They've simply never cultivated a fanbase in Asia, especially not outside Japan. That's why they haven't toured there. And, well, their weird Americentric touring pattern is another big reason why; come on, this band even underplays Europe, where they're most popular.
If the band got off their arses, they could definitely swing through India for 2-3 shows just off the back of the ex-pat population and whatever small local audience they have. India is so damn big that even a relatively small fanbase will sell out good sized venues. You don't have to look far to find other Western bands who've not only toured India, but played the biggest shows of their career there despite possessing no greater popularity there than elsewhere. Of course, those bands have taken a bit of effort to cultivate an Indian audience from early on, while U2 have toured so narrowly that they didn't perform in Italy until 1985, play a headline show in Finland until 1987, or go to Austria until 1992.