Blank DVDs have been around quite a bit longer than three years, and very few that age have problems. When blank CDs were new, there were also proclamations of doom and failing media, which by and large have not held true (I've got many 10+ year old CD-Rs and it's a rare that one that has problems.)
Regardless, hard drives often don't make it to three years of age - many less. (That's a big reason why most of the manufacturers only give a 12-month warranty now, instead of the 3-year that used to be standard - and why I've been much exclusively bought Seagate recently, for their 5-year warranty.)
If you have multiple hard drives storing the same data and are using them regularly, you're probably fine. What makes me nervous are the people (and I've seen 'em) who buy a hard drive (or several), fill it full of data, then stick it on a shelf somewhere, and expect it to be a safe backup a few years from now. Unfortunately, that's not a realistic proposition (plus it's far more expensive than DVDs or CDs.)
Tape is probably still the safest long-term backup, for better or for worse.