I think what he's trying to say is stacking more surge past the soft cap of 75% at the cost of alacrity is still more beneficial than stacking alacrity at that point. So basically an extra 3% crit multiplier is better than shaving .1-.2 seconds off a cast.
For me personally, I'd think its spec/playstyle dependent. Since I only have experience from the PVP side as heals I would say bubble spec is in lower demand of alacrity. Once I use rejuv, innervate, I'm usually busy throwing bubbles around and by then my CD's are over and i'm ready to throw more heals out. Only thing I'd want alacrity for is shaving my dark heal time down, but I dont use it as often in that spec since I'm prioritizing bubbles, rejuv, and innervate. So in that case a lower cast of .1 seconds is of little use to me.
Full heals on the other hand, I wanted a bit more alacrity since I am casting dark heal and reviv much more often.
That isn't what he is saying. If you read his other posts, he is convinced that you can trade alacrity for power and crit, which is not true. That said, stacking more than 400 surge at the cost of alacrity is silly. If you think saving 3 tenths of a second on your force lightning isn't worth the tiny bit of crit multiplier you get at that point, you really don't understand the S part of DPS.