The comment on Apple at industry conferences is a bit of a misnomer. I've seen at least 12-15 Apple engineers (from the backend Siri team) at MesosCon this year and last year when I went. In fact, they gave a talk[1] about how the re-did the entire Siri backend ontop of Mesos and it has became much more reliable as a result.
[1] https://mesosphere.com/blog/2015/04/23/apple-details-j-a-r-v...