Ford makes a mental note to ask Horseriver -- after he's put in the anti-magic runes.

"Because nothing from you is ever free!" Just because he can't see the strings doesn't mean they aren't attached. Appealing to his love of D, D & MD gave it away: it's too nice and therefore suspicious. "I'll manage just fine with what I have! There's no need to bring Dungeons, Dungeons and More Dungeons into it."