They're releasing the source. From the third paragraph of the second page:

"Other Web browsers could also employ Instant Pages, because Google has released the necessary code for all to use. "We are opening up the code because we want other browsers to implement it—it is good for the users and for the Web," said Singhal."

Even if this weren't the case, as drivebyacct2 said, this doesn't do anything to make us dependent on them, especially when compared to gmail or google docs.