Here are the actual numerical increases (average publisher difference, anyway) for those "top" countries for the last 10 years:
Country or Territory | 2004 | 2005 | 2006 | 2007 | 2008 | 2009 | 2010 | 2011 | 2012 | 2013 |
Mexico | 25,998 | 4,850 | 13,847 | 20,125 | 21,361 | 27,042 | 27,873 | 27,941 | 24,895 | 27,844 |
United States of America | 4,567 | 2,207 | 13,189 | 32,303 | 16,790 | 37,507 | 19,589 | 21,406 | 10,427 | 11,573 |
Congo, Dem. Republic of | 5,746 | 4,859 | 4,581 | 2,951 | 4,835 | 4,495 | 7,145 | 9,456 | 2,051 | 11,338 |
Brazil | 20,286 | 12,608 | 15,177 | 25,632 | 18,021 | 21,784 | 17,122 | 14,197 | 17,055 | 10,989 |
Nigeria | 4,993 | 4,465 | 3,998 | 9,144 | 8,322 | 9,226 | 7,297 | 5,361 | 8,414 | 8,338 |
Angola | 2,743 | 3,299 | 3,793 | 4,301 | 4,219 | 4,119 | 2,928 | 5,083 | 6,842 | 7,380 |
Philippines | 893 | 1,498 | 3,311 | 5,168 | 3,122 | 7,235 | 6,449 | 4,353 | 5,018 | 6,920 |
Colombia | 2,401 | 2,632 | 1,591 | 5,236 | 4,140 | 5,420 | 4,982 | 4,591 | 3,513 | 5,115 |
Venezuela | 2,467 | 1,128 | 1,369 | 3,890 | 3,103 | 6,052 | 5,192 | 5,820 | 4,137 | 4,614 |
Ghana | 2,428 | 1,887 | 2,657 | 4,881 | 3,703 | 7,035 | 7,547 | 4,384 | 4,367 | 4,307 |
Peru | 4,257 | 3,774 | 2,683 | 3,088 | 3,401 | 4,209 | 4,172 | 3,182 | 2,387 | 3,502 |
Zambia | 3,311 | 1,742 | 4,031 | 4,031 | 3,162 | 9,216 | 7,364 | 4,521 | 4,763 | 3,313 |
Ecuador | 2,563 | 2,283 | 2,507 | 4,219 | 4,038 | 4,302 | 4,146 | 3,445 | 3,087 | 2,979 |
Guatemala | 521 | 642 | 678 | 1,370 | 1,039 | 1,409 | 1,454 | 1,703 | 2,505 | 2,581 |
Malawi | 3,236 | 4,956 | 607 | 2,809 | 2,186 | 2,208 | 1,248 | 3,013 | 2,578 | 1,950 |