The GI magazine says, "Set two completely different spells in either hand, or put the same spell in both hands."
Either the GI magazine is incorrect, or this Dutch magazine is.
Maybe the Dutch magazine is saying, you can't use two completely different spells at the same exact time like you can with the same spells in both hands. But you can still have two different spells and use them one at a time.
That's the way I'm taking it. You can equip two fireballs to shoot one big fireball, or you can equip one fire and one frost spell and shoot each separately, but you can't combine them into a single fire/frost projectile.
...You know, it just occurred to me as I was typing this that he might not have been talking about equipping spells, but rather creating spells in the spell editor, saying you can't make a single spell with multiple elements, because of the secondary effects elements now have.