Does Every Webpage needs a domain name?

Well to clarify, a website can have one or more pages in it, like HomePage, Tech, Sports, Games etc. if all these section come under one branding (say ABC Tech, ABC Sports etc) you might not need a different domain name for different section. You can simply use sub domains (ABC.com/tech; http://abc.com/sports etc).

But in case you wish to have separate entities for different teams like ABC Sports, DEF Tech, GHI Games; its advisable to have different domains.