It's very difficult to get any unbranded game off the ground on the iPhone or any mobile platform. For every successful unbranded game on the App Store, there's 50 that failed. Most of the successful games are ports from another platform. And while they could've done a port, it probably would've sucked.
I understand where they were going, while Puzzle Quest is more like a traditional RPG (turn-based), this is more like an Action RPG (fast paced Puzzle Fighter style). It appeals to a large audience, puzzle and puzzle rpg fans, and for a game that is $5-10 I'm sure they'll get plenty of sales from Castlevania fans who are on the fence about it.
LoS is trying to open Castlevania up to a wider audience. I think this game has the same purpose.