Anyone with Internet access can put up a Web page. There is no censorship on the Internet. There is no one to check accuracy or authority of the author. There is no editorial board to approve articles on the Internet.
Someone can put a page and never update it or remove it.
For example take a look at this page about Dihydrogen Monoxide . It is water. This is one example to illustrate why you have to know what you are dealing with. Go to one of the Internet virtual libraries such as DeskRef to look up your topic in an encyclopedia or dictionary. For example a commercial page may contain very good information but knowing that it is a commercial page should make you question the bias and accurary of the information.