The biggest 'improvement' they did to IE in GDR1 is faking user agents so mobile sites think it's an Android browser so the site appears correctly. At the moment, IE on WP does 100/100 in ACID3. It does not support HTML5 as well as Chrome on Android though - but I really doubt that that's the main reason why Google stuff does not work well on it (as the previous example shows it as well).