Buddhism is the world's fourth largest religion, and while it does not hold view that only Buddhists will eventually attain enlightenment, it does profess that Buddhism is the only route to nirvana, or the state of awareness and existence through which a human being is freed from the cycle of suffering. In this way, Buddhists do not believe that any other religious practice or belief can lead to God. But it is interesting to note that Buddhists do not believe that non-believers will go to hell. Instead of employing fear as a tactic to draw more believers, Buddhism uses positive reinforcement, or the idea that nirvana can be achieved through the religion, as a major draw. The Muslim religion is also one of the largest and oldest religions in the world. it's like other Abrahamic religions like Christianity and Judaism teach that their way is the only way to God. They also believe and teach that non-believers, or "infidels" as Muslims call them, will suffer from their mistake (Hopfe and Woodward). In this way, Muslims, as well as Hindu's and Buddhists believe that their way is the most correct way to enlightenment or God.

Subjectivity

Some religions, like Buddhism and Hinduism leave room for the idea that their religion, while it is the most perfected path to God, is not the best way for some people to achieve enlightenment or walk on their path toward...

In this way, they are leaving room for other thoughts and beliefs. Christianity and Islam both believe in the suffering of non-believers. Both of these religions also believe to a certain extent, that non-believers need to be converted or even eliminated in holy war. Hinduism and Buddhism do not share these beliefs, and therefore can be viewed as being quite a bit more lenient toward non-believers.
It would be very hard to argue that the world's largest religions do not have a vested interest in attracting and keeping members, so it is logical that they would have built in religious beliefs and measures to do so. The idea that there are many paths to God is an idealistic one, and one that can be shared by many people in many different religions. But the actual evidence that religious movements truly feel there are many different paths to the same God or level of enlightenment does not exist. Personally, I feel as though all religions perform a function for humanity. They give humans order and authority, and help to add meaning to life. There is a basic human need for understanding the world around us, and religion helps to fulfill this need, independent of whether or not there is but one true way or path to God.

References

Hopfe, Lewis M. And Woodward, Mark R. Religions of the World. Pearson Education: Upper Saddle River, NJ. 2008.