Can anyone show me where a porcelain tile broke loose from Ditra or Kerdi in an actual install when it was installed per Schluter's recommendations (this includes proper prep of the floor)? Yes, you probably can if there were not one of those membranes underneath it. The Robinson floor test of DitraXL on a 24" joist spacing (really stressful), installed per Schluter's recommendation gets a heavy or extra-heavy rating, depending on the tile size. This is better than installation at 16"OC with a cbu...so, who are you going to believe? The manufacturer that has the independent TCNA test results to verify it, or someone like John Whipple that just doesn't like me or Schluter, or believe they know how to install their own products? Those test reports are: TCNA-303-06 and TCNA-153-09. You can look them up yourself, if you don't believe me.
As to bond strength, the TCNA also did some tests with porcelain tile with unmodified mortar, and came up with the following shear test average values of 277 and 365psi. Those test results are in TCA-073-03 and TCA-186-03. If you extrapolate those results to a 12x12 tile, that comes to 144*277= 39,888 or 144*365=52,560. I think, along with the long-term experience with their use AND the independent test results, John is blowing smoke.