Google has $44.6 billion in cash and short term investments at their disposal. Dropbox was recently valued at $4 billion. If Google could spend hundred of millions (or even a few billion) offering tons of storage space, you would have to think might consider doing so over doing something like trying to buy Dropbox. They would become the leader in the space almost overnight. At the very least, I would expect them to offer unlimited storage for movies and music purchased in the Google Play store (similar to Amazon).