The thing is, if the words "India rubber" are given a piped link, the user will be taken directly to a page titled "Natural rubber", which might confuse them, but if the words "India rubber" are linked as they stand, the user will be taken to the same page, but additionally bearing the text 
(Redirected from )
which explains why they were taken there. It is indeed unlikely that India rubber will ever be a separate article from Natural rubber; but that's not a reason in itself.