I think some people get all up in arms about it when larger publications do it, since it throws into question the validity of what they've written if they're trying to make money from referral links. However, the above is clearly someone's personal opinion , and I don't think that it should be scrutinised as if it were deceitful.
Would you also like Dropbox to add disclaimers to all their referral links reminding people that the person who sent them the referral is getting extra space as well?
1) when someone posts a book with an affiliate link and then says its a good book, it really clouds their intentions.
2) the link was obfuscated so you aren't really sure what it points to.
3) some people just won't click on an affiliate link.
By seconding his recommendation and providing a non obfuscated link everyone is better off. His recommendation has atleast been backed up and the user is certain of where the link leads to.
Everyone wins:)