Yes. People really need to be aware of phony "niceness". Attempts to minimize one's concern about people acting out of their self-interest are promoted the most by people who don't want others to suspect that they're acting out of self-interest.
They want you to believe you're paranoid, delusional, manic for considering the possibility that they may not have your best interests at heart. While it's true that skepticism can be taken to an unhealthy extreme, most people are too gullible, not too skeptical.
Ironically, promoting the "everyone is nice, don't worry, nothing can hurt you if you give everything away" perspective is itself evidence that they don't have your best interests at heart. Non-hostile people don't begrudge those who are attempting to practice reasonable due diligence and "deal hygiene". Good deals are good for everyone, and that means that you shouldn't need to worry about how "nice" something is or isn't.
This essay links out to a sister essay about how few business people are "mean". They certainly don't seem mean; conspicuous mean-spiritedness is not an attractive attribute, and you'll have a hard time accumulating power if you exhibit it. On the other hand, you'll also have a hard time accumulating power by being a bleeding heart.
As an investor, pg has an incentive to encourage founders not to worry about how much they're giving away. As a semi-prominent/powerful player in Silicon Valley, he also has a PR image that must be maintained to prevent an undesirable level of scrutiny from either the press or the government.
We should not forget that pg's self-interest is to convince others a) to give things away without thinking about it; and b) to maintain a public persona as a businessman-philanthropist with net social benefit, as opposed to a realistic cynic who used his advantage in wits to excel.