It would be incredibly difficult to armor a launch pad to survive an explosion on-pad, so they aren't. The real solution is to have multiple launch pads (the space shuttle had three), so that if one blows up on the pad you have backups you can use until the blown up one is rebuilt.

The energy released in the first few seconds of a controlled launch is not remotely comparable to the energy released by an entire rocket blowing up simultaneously. Also, with an explosion, the entire rocket, along with parts of the strongback and other structures it's attached to, become shrapnel. Superheated water exhaust is a lot easier to protect against.

The video points out two of the protection features, but they wouldn't do so well with a RUD.

The tower features - the hold-down arms, etc - are painted with a sacrificial paint. The idea is that it's the paint that chars and burns, rather than the tower features.

Then there's the water deluge system.

In the video, the rocket and exhaust is clear of the tower, and the fires are out, within 30 seconds. Neither the sacrificial paint nor the water deluge are designed to handle long-duration fires from a RUD.

After a 2014 Antares rocket failure, the launchpad at Wallops Flight Facility took 1 year and $15 million to repair [1].

[1] http://www.space.com/31412-virginia-launchpad-private-rocket...