Fair enough it may make the game 'Slightly' more interesting.. But why do they actually have them, I mean its not Major or Minor, i'm just wondering please help me out.
The main reason for Shiny Pokemon is mainly to make the game more appealing, and in a way, more interesting. This encourages you to continue playing the game, and to do so they have a low chance of appearing (however, if you are not happy with the 1/8192 chance, use Masuda Method to make it 4/8192). It could also be looked at as an acomplishment - since Shiny Pokemon are so rare, you would certainly feel good about yourself finding one (not to mention bragging rights!). It also keeps the game unique, giving it a vital selling point.
There isn't any correct reason for why Shiny Pokemon are included in the game, though it can be looked at as a way to make the game last longer in terms of '100% completing the game'.
Just to say you have a different color Pokemon than someobody else. Theres no real reason.
It makes the game more interesting as you said but it is also a unique selling point for the game which makes it more commercially appealing
It is a bit of what the Kyron and Scizornician said. But it is also a novelty when you get one. If you get one, then it is so hard to get one that it is suuuuper special! So it is both for novelty, another color if you do not like the normal color, and for selling appeal!
I think, by having such a low chance of appearing, the value of shiny Pokemon go up. That might explain Nintendo's reason of making such a thing, it's good for marketing and encouraging people to buy new games and participate in wi-fi mystery gift thingys.
See what I'm sayin?