Yea, the majority of films aren't presented in 16:9 (1.77:1) aspect ratio - mostly it is 1.85:1 or 2.39:1. Therefore, when you watch one of these films on your display then you will see black bars at the top and bottom. You do have the option on most video players to crop the image so it fits the image to the whole screen - however it has to chop off the side of the image to maintain the proper aspect ratio of the image - so this isn't always the ideal solution.
16:9 displays (like your monitor) were introduced first in the TV market before they crossed over to computers - since they offered better presentation of widescreen movies (compared to the more square 4:3) and eventually allowed 16:9 TV shows to become the standard.
16:9 is basically a trade-off for PC monitors - it is perfect for TV shows and films shot in 16:9, looks nice is games (though many would argue that 16:10 is better) and is superior to 5:4 or 4:3 for widescreen movies - however it generally isn't as good for desktop work (where vertical height and resolution are often more important than width).
You actually can get TVs specifically made for widescreen movies, for example Philips make the "Cinema 21:9 TV" - which is a big telly with a 2.33:1 aspect ratio. So using this TV for 2.39:1 films there are basically no bars. However, for other content the aspect ratio isn't ideal -as you can imagine.