Not true (or at least not ALWAYS true). Do you think corpdev guys are immune to anchoring? Here's a study:

"Take a minute and answer this two-part question:

1. Is the percentage of African nations in the United Nations higher or lower than 65? 2. What is the percentage of African nations in the United Nations?

This was one of the queries that Amos Tversky and Daniel Kahneman posed in their 1974 paper in Science called “Judgment Under Uncertainty: Heuristics and Biases.” It turns out that the answer you provide to the second question is heavily swayed by that first question. The average estimate for question two was above 45 percent. When question one was lowered from 65 percent to 10 percent, the average estimation of question two was dropped to 25 percent. "

Source: http://sethgodin.typepad.com/files/26237737-fixed-to-flexibl...

In a financial negotiation, setting an anchor can be powerful. a VC investment (and accompanying valuation) is an anchor.

I'm not sure the comment was about valuation it was about the purchase price. The buyer has to pay what the company is willing to take and part of that equation is how much the VCs that gave them $6M want for a return.