There was no PC stuff from Microsoft last time either. The PC goodies at E3 come from the Ubisoft and EA press events later in the show, and from the news sites working doing the rounds visiting the smaller booths.
Microsoft get bugger all money from games on Windows, but with Xbox they control the platform end to end so it makes them a fortune. The only reason MS keep up their efforts with Direct X on Windows is because, well, if they didn't then Open GL would dominate and then what's to stop developers building games for Mac of Linux machines. Direct X keeps developers happy and it keeps gamers on Windows, that's all MS care about in terms of PC gaming.
If Microsoft had taken charge of digital distribution/sales of games like Valve has through Steam then PC's would defiantly get a look in during their major Press Conference, but it seem they're content to concede that war.