They are slightly different joint though, so it will depend how you 'force' the joint to breaking point to make the claim. A tenon doesn't really hold the joint (although a wedged tenon could be said to exert sideways pressure on the mortice) and uses glue strength to hold the tenon in the mortice. A pocket hole joint uses a mechanical fixing to 'pull' one face onto another. The claim is probably true under specific circumstances, but not all circumstances eg a twisting force would be more likely to break the screw from the 'pulled' board than a tenon from it's mortice for example.
Horses for courses - I use both, but pocket holes can be difficult to locate in some instances and do not look as aesthetically pleasing. Great on ply or man-made boards for carcassing however, where they excel.
Steve
