The blog you listed is not using affiliate referral links to iHerb, they're just posting a direct link to a product page without using a referral code. For example, this is the link they're using on their most recent post:
On your site, for example, your post dated June 29, 2012 includes a link to "disse flakene på iHerb" using this link (rcode removed by me):
Everything after the "?" in that link is a referral code tied to iHerb's affiliate marketing program and is not allowed on WordPress.com.
You can link to products on iHerb as the other blogger is doing, but you can not use referral codes.
Let me know if you have any other questions.