They fail at even the most basic stuff too.
Like how when you launch a new app on the App Store, for the following 6-8 hours users get random errors ("not available on store", "not available in this country", sporadically missing from search, etc) when they try to download it as it propagates through the app store CDN. This even affected the recent OS X updates launched on the Mac App Store. Imagine if Amazon CloudFront worked like that!
And imagine if Amazon had to shut down their whole site when they updated one product like the Apple Store Online.