Originally Posted by
dminor
On a more technical note, the picture you supply shows a frame that did not fail at the juncture - -it failed in the manipulated tube behind it.
The pictured frame failed at the down/head tube junction in the HAZ (Heat Affected Zone) of the weld. It's the weakest point of any welded aluminum joint.
The cause: Rider error.
MTB frames are not indestructable unless they're built to withstand the abuse of dirt jumping or "slope style". Landing 50/50 (one wheel on the landing slope, one wheel off) will cause a frame to fail. As the OP mentioned, this type of failure is well documented.
Want your frame to last "forever", (or nearly forever)? Don't crash.