The Verge:

Apple’s own App Store support page reveals that 47 percent of all active devices are running iOS 8, an increase of only one percentage point from two weeks ago.

I would be willing to bet that the storage issues are a bigger hurdle for the average user than the mess that was 8.0.1, but the bad release is definitely playing a part, too. I know at least a few people who still haven't updated to iOS 8 because their device doesn't have the 3-5GB of storage required to install the update and are too lazy to make room or connect their phone to iTunes.