By the way, the sneak attack language is exactly the same in Complete Arcane (page 86). I haven't given it much thought, but I'd probably allow the same rules for Ray of Enfeeblement, Exhaustion, etc. Pretty much anything with an attack roll b/c I see no good reason to treat Enervation and Shivering Touch, which do stat damage and negative energy, as different and automatically superior to those spells.
I would hesitate to automatically define Power Attack as swinging harder b/c that restricts concepts. It surely seems that way, but it could just as easily be a haymaker (a broad swing) or a more targeted swing for a vulnerable point. Aiming for the eyes or neck means you're more likely to miss than aiming for the center mass. Also, the fact that something ignores plate mail doesn't automatically need you can't swing hard -- you can Power Attack with brilliant energy weapons. But, all of that is secondary to the ruling's potential to remove potentially interesting concepts.
For the record, just b/c it's RAW or a reasonable RAI, doesn't necessarily mean it's good for your table. It depends on the firepower you're comfortable with and what works for your party. My willingness to let someone Power Attack with Flame Blade or, more to the point of this thread, Eldritch Glaive comes from 2 observations. First, I'd hate to tell people that their only way to work that kind of build is through Sneak Attack or similar precision damage. I don't see how that's automatically much more benign than Power Attack. Second, I don't think the Glaivelock is a particularly powerful option. But, that depends on what else is on the table and what your baseline is. That's a good argument regardless of what the RAW is.
P.S.: the same would go with Decisive Strike. If you can figure out how to Decisive Strike with a spell, then more power to you. I can't see a good argument for distinguishing them. Again, the relevant question would be how powerful that ends up being. But, my gf was playing a Monk -- a totally powerful class we all know -- with Decisive Strike and she was doing a ton of base damage with a great attack bonus. So, I don't know how much of an edge it represents.