Y Combinator Founder Paul Graham Issues New Warning to Start-ups
I don't know if this is true or isn't true, but Google Ventures' counter arguments are red herrings:  "I don't know what Paul's thinking," Maris said.
  "It's just not true. Our portfolio speaks for itself."

and  "We've already closed investments on companies from this class,
  so they don't seem to feel that way," Maris said.

Neither of those things mean that what PG is saying is false. Google Ventures is a desirable investor and entrepreneurs would be willing to trade lower caps for a Google stamp of approval on their round. The question is whether it's a matter of their policy to quote a cap at half of a company's existing one, and whether that is an ethical policy. Because they are skirting the question, it certainly makes them look guilty to me.