Microsoft decided that due to their new interoperability initiative, they would reverse a previous decision to make IE8 default to the IE7 engine, instead of supporting standards-compliance by default. No article or musing I have yet read has delved into what is increasingly likely, the reason for this sudden change in decision -- and that is this: the mobile web is coming.
The iPhone & iPod Touch have caused an influx of mobile web browsing the likes even Google had not seen. Many smart phones have an Internet browser, only Apple's has had the interface to make it desirable to use to non-geeks in a way that can be measured in server-log lines, and not in forum-posts by iPhone detractors.
Microsoft have a mobile-browser, how are they competing with this? They are not. Mobile IE is unusable compared to the development buzz surrounding mobile web-apps using Safari, which supports a full compliment of standards.
If Microsoft were to default to the IE7 rendering engine on their desktop browser, how would this affect the rapidly rising mobile browsing market? They would simply get left behind.
Their mobile browser would have to ship both IE7, and later engines to maintain compatibility with a web they were partly defining with their desktop client. Any new fancy features their mobile browser could offer to compete with Safari would be stymied by the fact that the majority of websites would be coded to the IE7 engine by unaware novice web developers and out of date web development packages; all the time while web developers explore new avenues of web apps using the full set of standards open to them on Apple's handheld via iPhone-only websites.
Microsoft, IE8, Internet Explorer 8, Internet Explorer 7, IE7, Interoperability