I don't know that I agree with that statement. Just because having more than one wife is permissible in Islam, that does not necessarily mean that it is following the sunnah to actually do so. If this were the case, it would be frowned upon to have less than four wives. Since genarlly there is about the same number of women as there are men, it would mean 3 out of 4 men would have no wife at all and 1 out of 4 men would have 4 wives.just normal but like to follow the sunnah and have a co-wife.
This is already a problem to a lesser extent in China due to sex-selective abortion of female fetuses.
http://www.msnbc.msn.com/id/16593301/#storyContinued
China will have 30 million more men of marriageable age than women in less than 15 years as a gender imbalance resulting from the country’s tough one-child policy becomes more pronounced, state media reported Friday.The tens of millions of men who will not be able to find a wife could also lead to social instability problems, the China Daily said in a front-page report.