I haven't read the article yet, but it is not a new discussion. If the material above the drainage layer is suitable, and if the drainage layer itself is suitable, water will be retained in just the same way that a kitchen sponge does despite your holding it in the air. The critical issue is those 'suitabilities'. Consider if the upper layer is the same material as the lower one - say all gravel - then it will all drain well. If it is all clay, it will drain badly (shrinkage aside). I think old clay crocks make a good drainage layer because the material is very easily wettable (by the layer above), and hence can 'conduct' water downwards. ...If the upper layer wants to let it go. If the upper layer is naturally water-retentive, a drainage layer below it won't help that much.
Back to conducting...
I think one has to think 'outside the pot', as it were. Below the drainage layer, there is the hole(s) in the pot and the pot base itself, and then whatever the pot is standing on (soil, concrete, legs, etc.). It is not much use to have a drainage layer that conducts water itself if the water has no easy way to leave the drainage layer. The gap constituted by the hole in the pot can be a barrier to flow! Yes, it will let water out under the pressure of its own weight, but it can stop the slower drainage driven by surface tension. If the pot is (unglazed) clay, resting on soil or capillary matting, it will conduct water away OK.
So, IMO, if you want to promote good drainage in a pot of soil:
1. Make sure the growing medium is itself at least fairly well drained.
2. Connect the growing medium to a water exit outside the pot, ie. use an unglazed pot resting on soil, with or without a drainage layer; if using a drainage layer, ensure it is not water repellent (eg. polystyrene); if it is not possible to rest the pot on the soil and/or not possible to use an unglazed pot, then put a strip of capillary matting through the hole and lead it down or across to some soil or other absorbent exit.
3. Allow for immediate drainage of excess water under its own weight by having the pot hole(s) open to air - which can mean lifting a pot off the soil (obviously contradictory to point 2), but capillary matting can make the connection again. I have some old clay pots which have the drainage holes at the sides rather than underneath - they are ideal for allowing pot-soil contact while keeping the holes open to air. But you see few of them these days.
4. Consider other factors. It can be a good idea to use perforated zinc over the drainage hole - to keep weevils, larvae and some other critters out. One can do so while still having a strip of capillary matting in place. Put a disc of capillary matting in the bottom of the pot in addition to the strip - helps gather water from across the pot and if the potting medium is prone to shrinkage (hence watering water going down the side), it can help re-wet the medium.
(Note: capillary matting can become less hydrophillic as it ages, partly due to the chemicals it has absorbed over time; it may need replacing. Also, roots can insinuate cap. matting, which might be an issue at repotting time.)
That's off the top of my head; my apologies if I have forgotten something obvious.
