Reviews, reviews, reviews...

Question: Identical HDDs in NAS Server?

I just purchased a dual bay NAS and I also purchased two identical Western Digital 2TB hard Disks (model WD20EARS to be exact). They are both mirrored using RAID level 1. Now I've been told by a friend of mine that I should have two different brand drives of the same capacity instead of identical ones just in case they are both faulty and both die on me at the same time. Obviously I'm a bit paranoid that he's right but I want your opinions please.