@ShimizuA: You're kinda missing the point here. In Saudi Arabia and most other Muslim countries were polygamy is still practiced (some Muslim countries have outlawed polygamy due to having adopted more Western values), the cultures still cleave unto the "husband = family's breadwinner" ideal, to the point of putting a lot of pressure on husbands even if the wife/wives have well-paying jobs.
It's totally different in your average harem anime/manga, where the characters hail from Western(ized) cultures in which the "husband = family's breadwinner" idea has become/is becoming out of vogue nowadays due to full-time working women becoming mainstream, at least in comparison to Muslim cultures.
@daijokay: You could say the same about there being too many monogamous marriages where the husband is both a cheapskate to his wife and children despite having more than enough money to support them and horribly abusive. It's not an inherent problem in polygamy per se; it simply magnifies an existing problem.