I also agree that good female role models are important. Selling technology and engineering to girls as a viable route to take is the key to increasing gender equality in the field.
This said, we also need to accept reality. The reality is that the experts in their conference's area are primarily men. Based on my experience, I'd be willing to be that somewhere around 95% of people who work with the database technologies the conference targets are male. Assuming that only a small proportion of people who start working with a particular technology end up being considered "experts" in the area, it's fairly obvious that the pool from which to select women is diminuitive compared to that from which to select men.
My experience of technical presentations is that the level of expertise the person giving the presentation has directly impacts the quality of the presentation. I'd argue that by taking the approach they did singnificantly diminishes the quality of their conference. This isn't unique to gender - if they'd selected based on any under-represented group they'd have a similar outcome.
Promoting female role models in tech is hard. Perhaps a compromise - ensuring female representation was at least a certain proportion - would work. Affirmative action is always a tricky area to deal with, and it is always more complicated than it first seems.