I don't get Google

Why is Google becoming more then a matching engine (of information, advertisements, etc)? Why are they starting to compete with some of their (potentially) most profitable partners? It's a vertical and horizontal integration I don't get. I understand their mission, organizing the world's information, as long as they are indexing things and make it easy for me to find what I'm looking for. Whether that is an ad or a website, on a map, through Froogle or Base, or in a partner's domain. But more and more they are becoming a content platform themselves. Why do they have to buy YouTube to organize the world's information? They need to index YouTube's videos, not buy their platform. I didn't understand it with Blogger, Orkut, GVideo, GTalk, Gmail and Picasa either. I do understand the business opportunity of those services, certainly when they are well integrated. Hey, I'm using almost all of them;-) But why is that Google's business? They have a great platform to enable, facilitate and profit from such businesses when started and run by others, but why does it have to be their business completely?

The only reason I can think of why they are doing this is because they see a future where a small number of companies (Yahoo, Micrsoft, Google) will dominate the communications, sharing, collaboration and publishing business with very tightly integrated offerings for both individuals and businesses. And that each of these businesses will have their own matching engine as a monetizing driver since all services will be offered for free. Google already had the latter, so they are now building and acquiring the first to make sure they won't be out of business if this future unfolds. But will that happen? I don't think so. Tight vertical and horizontal integration organized in one company is not a natural model for doing business online.