Don't forget that live view also gobbles up the battery.
As some have pointed out, the viewfinder gives the actual view through the lens and has been this way since the SLR was invented
The more expensive (pro) cameras have a 100% viewfinder but most 'lesser' models will have anything from 95-98% of the actual scene visible. IMO this is no big deal.
It's also easier to hold the camera steady when you use the viewfinder, as holding it away at arms length will cause camera shake, especially if you have a big telephoto-zoom fitted (unless you use a tripod!) You also look a bit of a d*ck holding a DSLR this way!