Final Fantasy maker Square Enix doesn't only make Final Fantasy. The Japanese company also has an anime and manga division, responsible for titles like Saki and Full Metal Alchemist.
When division head Kouji Taguchi was asked why manga sales in the US were still considerably smaller than in Japan, he replied:
The best sellers in the US were Full Metal Alchemist and Naruto, but these only sold a tenth to a twentieth of what they sold in Japan.
I think the main reasons are as follows:
1. Fewer copies are printed and those that are get sold at a much higher price, from $8.99 to $12.99.
2. Children don't get as much money, their allowances are just smaller.
3. The other reason is location. If you live in Tokyo there will be 3 bookshops nearby, which you can easily cycle to. In the US there aren't any, they can only buy on a weekly trip to the mall. Even if anime is highly popular, they just don't visit the stores to buy manga often.
As website Sankaku Complex points out, it's interesting that Taguchi focuses on distribution instead of simply stating that Japanese and Western tastes are different. Taguchi also went on to state that manga publishers are increasingly moving forward to digital distribution.
"Publishers such as Shueisha, Kodansha, Shogakukan and Kadokawa are setting up a digital platform on the PSP for distributing manga," said Taguchi. The Square Enix exec doesn't think this will catch on in Japan because prices are low and there are many shops selling manga. However, this form of distribution could very well catch on in the States.
誠：劇的3時間SHOW：『咲-Saki-』『鋼の錬金術師』の田口浩司プロデューサーが語る、儲かるアニメの作り方 (1/6) [Business Media via Sankaku Complex — Image NSFW] [Pic]