THE BOTTOM LINE: It seems to me that Apple's Time Capsule is a good tool for restoring working files from time to time, and emergency system restores, but it should absolutely NOT be trusted as the only system archive, let's say for precious family photographs, documents, and videos!
I just experienced unexplained destruction of my Airport Extreme Time Capsule backup for my MacBook Pro.
There is nothing wrong with my TimeCapsule hardware, which has continued to work perfectly for my iMac, and has worked faultlessly for two weeks since I deleted the corrupted MacBook Pro backup and created a new one. Something happened to corrupt the MacBook backup while it was processing. As Pondini suggests, it may be an interruption in the wireless connection. Who knows? All I can tell you is that it processed correctly @ 6am, but by 8am the backup was irreversibly corrupted. I was online the entire time, checking email, using Safari, never lost the connection.
After a finally giving up on restoring the corrupted sparsebundle (and I tried many different methods in terminal after Disk Utility and Pondini's other suggestions failed), the TimeCapsule is again working perfectly - but I certainly do not trust it any longer, that's only logical. There was over a year's worth of backups on there! Thank G-d I have two Macs, with redundancy of my data on the other Mac and its backups (which are still working just fine on the same Time Capsule).
When we say, 'were you connected wirelessly?' while conducting the backup as a possible reason for the fault, OK.. OK.. that's like being asked whether we were driving on a dirt road when our engine threw a piston. Either Airport Extreme works wirelessly safely, or it doesn't. I'm not going to have Internet cables laying around the house from the Macs to the device. The Wireless connection was explicitly stable and undisturbed during the fault. There could be some glitch in the system logs to reveal I suppose.
Again, don't trust this device with your precious personal computer file archives - back them up periodically on an offline disk.