If a Necromancy spell isn't a necromantic effect, its hard to say what is (esp since no one seems to know of a list somewhere in some book titled "Necromantic Effects"). One thing AE did was include more descriptors; something similiar came up in one of my games when a character that was immune to spells with the Negative Energy descriptor got hit with a Ray of Enfeeblement; basically I had to read the spell and guess. Most (though not all) necromancy spells would have the NE descriptor if you ported them to AE, and it's pretty much synonymous with "necromatic effect". (It even has the same initials, though thats really just a coincidence. Or is it?!?)
I think this may be a case of the game designers using two slightly different terms to mean the same thing, and not expecting any confusion to arise. Necromancy spells have necromantic effects, by definition. I can't think of another way to interpret it. Since there's no listing for "Necromantic Effects" in either the DMG or PHB (and I'm too lazy look any further), I'd have to assume that any spell with a by-line of "Necromancy" qualifies as a necromantic effect. (This includes all Sor/Wiz spells of the Necromancy school, as well as the Inflicts, the Death Domain, and the spell Deathwatch-- which is oddly [Evil]. Its apparently evil to know how wounded your compatriots are.)
Though in glancing over the books, I am reminded of two things. One, the expanded list of descriptors in AE clears up a lot of confusion in this regard, and Two, I cannot for the life of me figure out why the Fear effects are in the Necromancy school and not Enchantment.