How many 2003 US produced movies made up top 10% of annual earnings?

*Note: By 2003 it is assumed that you mean films released in 2003. 
The source used (Box Office Mojo) counts movies that were released in
2003 and continued to sell tickets in 2004.

The total overall box office for 2003 was $9,185.9 million.

"The Lord of The Rings: The Return of The King" took in $377.0
million.  This made up 4.1% of all earnings.

"Finding Nemo" made $339.7 million.  This made up 3.7% of all earnings.

"Pirates of the Caribbean: The Curse of the Black Pearl" earned $305.4
million.  This made up 3.3% of all earnings.

"King" and "Nemo" together accounted for 7.8% of all earnings.

"King," "Nemo," and "Pirates" together accounted for 11.1% of all earnings.

I hope this helps.

Sources:
-Total Box Office Business By Year
http://www.boxofficemojo.com/yearly/
-2003 Box Office Chart
http://www.boxofficemojo.com/yearly/chart/?yr=2003&p=.htm