I know tying is a key part of monopoly abuse, but I think reinforcing is more important. Take the deal where Google translates the patents for the European Patent Office; it gets paid, it gets to index the data to extract knowledge it can use in the search algorithm and it gets parallel documents it can check and then use to improve its translation algorithm (I'm just assuming the translations will be checked because even in a closed domain, unchecked machine translations of patents sound like a lawsuit waiting to happen).
It's not a crime just to be big; the issue is what you do with your size and whether you do things that unfairly keep others out of a market.
Everything Google does in all areas of its business (apart from possibly Google Apps in enterprise and government, and it may apply there too) is designed to either put Google ads in front of more searchers on more platforms or to give the Google search engine more training data in order to improve the search engine that puts ads in front of searchers.
Gmail, Picasa, translation, the Google Maps sensor probes you have to take to put Android on the phone you sell – they all get more data for Google to crunch. Their business model is transforming the information of the world into a source of targeted ads. By having a bigger index, Google gets to have a bigger training set for its engine. And how much it promotes its other services that funnel training data to the engine has to matter as a question of reinforcement; the circular nature of what Google is doing doesn't work in isolation.