Yes, they've become much faster, their capacity has grown by orders of magnitude, and the price per byte has fallen by orders of magnitude. But the invariant is that a given disk still has a significant probability of failure during its lifetime. I've seen several PC IDE disks fail in the last few months. One of my past projects involved storing movies on disks. Disks that were put into production stabilized to failure rates of just several per month in a thousand-drive video server.
All disks wear out and fail.
The other scary trend is the proliferation of multi-gigabyte disks in personal computers. It's one thing to have tens of gigabytes on a shared server maintained by a staff of administrators, but when every Tom, Dick, and Harry gets 10GB on a personal computer, there is going to be disaster sooner or later. It's too easy to collect software and data. At least stamp collectors have to physically exchange albums and provide shelf space for the collection. Trusting huge cheap disks by itself isn't a problem, but without backups it is.