Not the OP - but I think you miss the relevance of point 5. Tech is littered with the irrelevant remnants and skeletons of "giant unstoppable forces". Look at Sun - in the 90s they were unbeatable, by 2004 they were quickly growing irrelevant. Oracle seems to be on the way out. Cisco too - they haven't done much exciting in a while, in a lot of circles they are viewed as the company holding networking back.

Other companies no one could unseat:

* DEC

* Xerox

* Apple (a couple of times)

* Corel

* Lotus

* IBM (a couple times in a couple fields)

* And on and on.

The point is that given a bit of time, Google will mess up, someone will come up with some new tech, and/or google will implode under it's own crushing weight.