I think you'll find that coca cola and Mcdonalds are in the top 5 corporations in the world. McDonalds used to make thier own 'McDonalds Cola.' Thats why when you used to ask for a coke, you got the standard reply of 'Thats McDonalds Cola.' McDonalds realised, after years of peopel getting pissed of with hearing that reply, that people wanted the real thing, not a weaker version. They also wanted drinks, such as sprite, that they couldn't produce. Its just simply business. Two of the largest corporations in the world get together and sell their products at the same time, making each others profits even bigger. (Coke is now as recognised a word as ok., and known by vitually every one on the earth.)
I do not believe that Coke is up to anything more than boosting its profits. McDonalds are just doing the same by selling Coke.
If you want more information check out their (propaganda) web sites.