iPhones are very easily identified and labeled through the use of numbers which tell you what iteration it is. An iPhone 4 is obviously older than an iPhone 5. Android device naming, on the other hand, is all over the place. Galaxy, Nexus, Infuse, Aspire, One X... it's too cluttered for a non-tech savvy buyer to distinguish which one is better. The only way to tell is scouring spec sheets and doing research.
So again, if I was Google I wouldn't want to run the risk of someone using a non-flagship device such as the Infuse 4G and thinking that was the best my company had to offer. Give them a Nexus 4 and they'll say, "Is this really Android, too?"