Well, at least part of the stage was full.
Photos of empty seats from different angles. A few as Obama comes onto stage. Some with him hugging Michelle. You can clearly seat empty seats on the upper levels along two sides.
1. http://imgur.com/zovvN.jpg
2. http://imgur.com/jLAlF.jpg
3. http://imgur.com/crORC.jpg
4. http://imgur.com/Kxymy.jpg
5. http://imgur.com/OhesA.jpg
6. http://imgur.com/hbYlv.jpg
7. http://imgur.com/wkSZc.jpg
8. http://imgur.com/eiRen.jpg
9. http://imgur.com/NlG0v.jpg
10. http://imgur.com/Zcg2E.jpg
11. http://imgur.com/DK6Iv.jpg
12. http://imgur.com/7z8Dn.jpg