I'm a little late to this discussion, having benched my mage for the forseeable future I haven't been in the mage forums often lately.. anyway, apologies if someone already said this, but faster casting does also have the benefit of being able to move more often as well as finish casts more often before having to move. This can functionally be a significant dps increase for a player that won't always show in math or sims. Blade lord is a good example of a fight where you may be required to move at any point in time, so I can see why he might not use the glyph. That, and they've already full cleared, so its possible that he's just doing what he prefers now that it's farm content. Its unlikely that he has better math than the rest of the community is privy to.. as has been pointed out he's probably just playing really, REALLY well.
Last night I tested haste to the 17th NT tick. This required I gem straight haste in a few slots.
I also removed the icy veins glyph.
My guild took a retarded pill and I didn't get any good parses, but my personal DPS definitely improved, but the entire flow and feel improved as well. NT ending quicker helped shake up the rotation in a positive way and the numbers followed well. The faster casting on the icy veins every 90 sec made movement better and keeping the debuff up on the target better.
On Garalon Heroic 25M it really was noticeable how great the NT tick damage was and despite ice lance cleave not working (grrrr fix it blizz!), it just felt better.
See my armory for more info, 10,124 haste rating. 18th NT tick possible in heroic gear! I'm going to find a spriest and go to a dummy, get EoT, Time Warp, and Icy Veins all up at once and see how many NT ticks I get.