Blu-ray is the format that's replacing DVDs, but it appears that it arrived too late to be the last major optical format for computers. That title goes to the DVD.
According to iSuppli, only 3.6% of PCs sold this year were shipped with a BD drive. And by 2013, that figure is only expected to rise to 16.3%, far from a solid attach rate.
With install discs being replaced more and more often by downloads, movies being downloaded instead of watched on disc and the insanely cheap price of mass storage, it's no wonder people aren't willing to shell out the scratch for a BD drive. They just aren't that useful.
The era of physical media is over, and Blu-ray was just too late to the party to really catch on like past formats. It'll still have a relatively successful life in the home theater world and with enthusiasts, but it'll never come close to touching the saturation level of DVD. And really, that's fine with me.