Fong was trying to 'beat' the ES sound with his new flagship, perhaps the Abyss offers a different sound which is down to preference rather than levels/degree of ability in certain sonic contexts. The former is 'better' to showcase as it can be classed as more objective.
Either that, or as you hint, the Abyss does some thing(s) better, which they don't want highlighted at the demo. Bass, and perhaps mids (when driven with the right amp/dac).
maybe fhey cldnt afford the abyss. its quite pricey afterall