How come there isn't a buy this licensed manga here link?. Surely it would benefit the mangakas, let people find a retailer quickly and possibly earn the site some money for the referrals?

Or maybe a single page on the site listing online manga retailers internationally (UK, US, Germany, Japan, Korea, etc...)

I've considered approaching retailers and working out some sort of affiliate program, but I just never got around to it... I think working with individual publishers themselves would be rather difficult and complex..

If you worked with retailers, you'd have to not show releases for licensed manga.

Simply, you can put an Amazon link or something to a site where you can buy the licensed manga.