Xbox tend to 'win' showcase wars because the people who put them together seem to have relatively good taste and a finger on the pulse of what the hardcore players actually want to see. Their lineup isn't actually that amazing, they just know which third party games to show and what indie games look good enough to get people's tongues waggling.
When you break it down, most of what is shown is either a) straight up multi-platform, b) a timed-exclusive release or c) inevitably going to be multi-platform via Project Latitude. But it makes for a nice showcase and so that is what they will be rated on. Sony on the other hand can't put together a good presentation to save their lives. They're either too short, too light on first party content or are filled to the brim with shit no one cares about except Resetera and Men_In_Boxes.