It is simply because you are not even allowing yourself to see the benefits of having an indepth game on a mobile platform. Baldurs Gate is the perfect example of a game that has complex game mechanics, yet low system requirements, so it should be possible to port to a mobile device like the iPad. I feel that a turn based game would work better (like say Fallout, Civilization, or HOMM) since it will be difficult to use the touchpad in real time the way you would with a mouse and keyboard, but it is a slow paced game and the mechanics are turnbased (although constantly running).
The point is simply that there aren't many complex options on mobile devices that aren't Gameboy type devices (I can't think of what a mobile gaming device would be called, perhaps just "mobile gaming device"). I for one would like one. I have times when I would like to do something more than a simple puzzle while I am stuck somewhere by myself (like on an airplane, or when I am laying down with my daughter trying to get her to fall asleep.) Simple things like Angry Birds, or Cogs, or Drag Racing just don't keep your attention for very long, and get boring quickly. A complex game you can get into like Baldurs Gate on the other hand could keep you interested the whole time you are in the air.
That doesn't mean that the iPad would replace the PC as your primary gaming device, but it just means that there is no technical reason you can't play indepth games on the iPad. I can think of plenty of reasons to play those games on the iPad as well. Saying that people likely already have the game on their PC so they aren't likely to buy it on the iPad is kind of missing the point. The reason for having it on the iPad, isn't to be able to play the game when you are at home with access to your PC, but instead to be able to play it when you don't have access to your PC.
I fully and uniquely understand the value of such a game.
What you are not understanding is that the market for such a game would be small. The reason most mobile application/games are simple GBA/DS type games is because that is what the market generally goes for. It isn't generally that 'if you want something more complex, you have to go to a PC' it's 'Most mobile gamers want something light and easy and that you can get into and out of quickly'.
What I have been trying to explain for days is that the market just isn't there. Yes there are some people who would buy/play it but most Ipad gamers simply aren't interested in that. You are the exception. So would I be if I had an Ipad. And I have looked. I own a PSP and a DS precisely because I am looking for that elusive 'Complex and compelling' mobile game. And that is precisely why I won't buy a PSVita or a 3DS, because look though I may I haven't found it. Not because the hardware doesn't support it. But because the community doesn't (as a whole) want it. However, as I have explained, as much as I would love it to be different, the exception does not make the rule.
I would LOVE it if more Ipad and mobile phone gamers wanted more than Angry Birds. I do a LOT of traveling myself and have a gaming laptop in as much as such a beast exists. And I run Baldur's gate on it. I would love nothing more than to be able to sit in the airport and play Skyrim. Only I know that an Ipad wouldn't take that. If it did, I would own one in a second.
And I would love BG3! But I consider the market this is being created around and I don't see a lot of consumers. And then there is the cost. But we have had that discussion.
Maybe I am wrong. But simply put, I see the average Ipad gamer as a 'casual' gamer. Certainly the vast majority clearly are or there would be a whole host of more indepth games for that platform. Baldur's gate is not Huge in the casual gamer community. And even if it were, there is a current solution that, for the price of the PC version and a free app, you can play on mobile devices (or is there a cost for that?) In either case, why pay $40 or more when you can pay $15 for the same thing? Convenience? I see that as an even smaller market.