Is iPhone OS (IOS) game on iTunes selling more than computer games on Steam?
IOS platform has iPhone/iPod Touch/iPad → very large user base and willing to pay
Steam client available on Mac and Windows → also large user base but also pirates everywhere. 
For me I bought games on both platform, with similar quantiies on each.
I ask this question because I am consider should I make my first game for iPhone or for computer. :roll:
I would say that as far as piracy goes, there will be plenty of it to go around on either platform set. Really, what should determine where your game goes is the target market (age groups, genre, casual vs. hardcore gameplay), control scheme required to make it work well (keyboard/mouse/x360 gamepad, vs. touchscreen or multitouch, precision/responsiveness/quickness of input needed), type of game (genre, graphics power required), and finally, pricing/cost/labor required to make.
For example, a basic physics-puzzler might work fine on an iDevice or Android phone since it wouldn’t require rapid inputs or amazing graphics to work well… but a heavy-duty 3rd-person action game with lots of enemies and explosions wouldn’t necessarily work so well on a small screen with limited input options, nor would it be as popular to iDevice/Android gamers as it would be to PC gamers on Steam/etc.
It really depends, as I said :). Also to consider is the cost/time/labor needed to create and return on your investment. Lots of research to do… just keep in mind that there’s piracy on both, and really, if someone wants to pirate something it doesn’t really matter what platform it’s on: they’re going to do it anyway. The best you can hope for is to convert some piracy into sales with subtle reminders that the game/app isn’t free and took resources to create, and a quality product. Other than that, I wouldn’t worry about piracy rates on one vs. the other: it’s just not significant enough a difference in my opinion.
Make them for both?
2x more profit 
If it’s possible I would certainly try to make a port for Android/iDevice of a given game… or even a scaled-down version for the handhelds. It’s great cross-promotion, and as you said, it increases your audience and potential profit ;).
I’d suggest starting out with mobile. You can keep the scope of your game down (in design and time invested) and still have a chance of making a little money. For computer, you’re going to have to make something much bigger just to get people’s attention.
Thanks all for reply. 
I found terrain is not support on iPhone, how to build terrain in iPhone games?
And compare the build size of iPhone Basic and Pro, how much smaller actually?
Modelling software where you build everything.
0-3mb kind of. The important part is that this is also saved on the runtime memory, not just the disk / download