It's too soon to tell whether Croll's acknowledgement that user customization is desirable represents a shift away from the autocratic design tradition that has served Apple well over the years.
But at the very least, Apple is trying to make Safari more competitive with Chrome and Firefox, which have built a loyal base of users in part through their extensibility.
Safari 5 also looks a lot like an attempt to undermine Google's ad-supported business model, which happens to threaten Apple's revenue from software and subscription sales.
With Safari 5, Apple has become the highest profile promoter of ad blocking among its peers. On the Safari 5 Web page, Apple notes that the Safari Reader button can make "articles instantly appear in one continuous, ad-free view. So you can read without distractions."
Apple also appears to be eager to provide instructions to developers about how they can create Safari Extensions that block content. One of the prominently featured sample code projects in Apple's Safari Dev Center is the Blocker Safari Extension.
Apple is also making a point of featuring Microsoft's Bing extension in its press release and in its Extension Gallery. The absence of Google, the most popular search engine in most of the world, is conspicuous.
Apple's iAd service for mobile advertising on the iPhone initially appeared to limit the ability of Google's AdMob to serve iPhone ads, but the inquires of government regulators appear to have forced Apple to back away from enforcing rules that would have hindered competitors.
Safari Extensions do not work on the mobile version of Safari, found on the iPhone, iPod, and iPad. It remains to be seen how eager Apple is to allow users to customize the iOS device experience by blocking distracting iAds or Web ads.