It seems many people, especially younger people, no longer want to attend church. Going to church appears to be a factor in determining whether one is "religious." But religion has very little to do with true faith and spirituality. I know many people who have great faith in God and are deeply spiritual, who do not attend church. They can commune with God on their own, without all of the traditions that seem outdated.
Norway did not suddenly lose 25,000 members after the new online system, those people were gone long before this happened. To be frank, many many church goers attend service more out of a sense of obligation and guilt than dedication. Many religions maintain very conservative and ideas which most of the world has moved on from. You don't need to be religious to be a good and moral person.
Yes, people in general are becoming less religious for a number of reasons. Because of advances in health and science, people now live longer and fear human mortality less, so the need for a religion to provide comfort and the promise of life after death has diminished. Also, many religions tend to be conservative, with holy books based on lifestyles that made sense thousands of years ago. These old texts and religions seem less relevant to people in the modern world, yet new religions and lifestyles have not been formed to make up for that cultural gap, so people are simply leaving old religions. Finally, it is now easier to identify as a member of many religions while not actually belonging to a church or other religious community. Our notions of faith have changed vastly: once, people believed that religion was about performance of certain ceremonies and active participation in a religious community. With the rise of individualism and changes to theology, most people now believe in having personal faith in a deity rather than participating in a religion.
Yes, people are moving away from traditional churches and thus becoming less religious. However, they are getting more spiritual. There is a difference. Spirituality is personal, while religion is group-oriented. The fact that 25,000 people left Norway's biggest church points to this new trend in religion and spiritual practices today.
Religion is merely how cultures keep their governments in check. The minute their governments actually provide a certain standard of living and comprehensive safety nets entire countries simply stop attending religious services overnight. The opposite is also true and in China today long avowed atheists are now converting to Christianity in record numbers complaining they can no longer trust their government to instill values in their children. Notably, both religious totalitarian and atheist communist states are now largely relegated to the third world, while the US has become the defacto empire by maintaining a strict separation of church and state and promoting rugged individualism.
The increasingly secular countries in the majority of the developed world have only managed that feat by depending on the US to pay for half the costs of NATO and the UN so they can spend more money on their population rather than defense.