Or he's spec'ing based on their current encounters. SS is pretty useless for add kiting. Imagine life platform for HM conclave. He has piercing howl for his adds, and can intervene the zephyr tank for another 6 second CD there with the safeguard he picked up over HR. The buff on the boss lasts for 15 seconds, which means that the MT on life platform can typically cover 10 seconds with a personal CD, and having intervene covers the last 5. Yes, you can use externals from healers to cover the last half, but remember that they are typically rotating for the frost debuff, so it can be difficult to ensure you have one on your platform when needed. Heck, a 225% damage bonus buff... take all the externals that you can get.
Same-style arguments for heroic Maloriak.
This always comes up, and it gets so frustrating reading post after post about ideal specs. Look at what your guild is working on. Look at your role during that fight. Spec/glyph/consume accordingly.