Apparently, a DVD-RW can be re-written several thousand times before it fails. I am not sure why manufacturer's don't say this on the label.
Let's say that you recorded a daily TV show and viewed it later that day, only to record over it again the next day. That would be 365 such rewrites during a year. Let us assume that you did not remove that disk from the drive, so it was never handled. That means that your disk would remain clean, and repeat the re-recording for 15 years or more.
But you see, handling a DVD-RW is the hard part. If you removed it from the recorder all the time, fingerprints would eventually ruin it.