However, I'm not so sure if the average consumer (the target audience for the Kindle) will even think twice about this. Consider cable TV; People happily pay for cable TV subscriptions which still include commercial ads. They (arguably) don't get in the way of the end-user experience, yet they subsidize the costs for TV programming. Likewise, the ads on the Kindle are limited to the lock screen and kept out of the way of the actual user experience.
Also note that Amazon has deliberately chosen to not offer a higher-priced version without ads. Without an option to pay more to remove ads, the consumer will never have to debate whether or not the annoyance of the ads is worth $30 dollars to them. Instead, the ads become a fact of life and are accepted without question by the end users. Even better, it widens the Kindle advertising demographic to include those with the most disposable income who would otherwise pay to remove the ads. Smart move.