Ok, I think we agree on the iphone part, that due to its small sized screen it is not suitable.
On the ipad now:
1. there are many devices from other companies making tablets. Why should riot make it only for the apple one?
2. do you reall want to use your right hand as a mouse while you are using your left hand to hit keys like crazy and do all of that on a touch screen for 20-40 mins? even if you had the keys in the left bot corner and the mouse scroll in the right one, using your thumbes for both, wouldn't you hands hurt after ten mins or so? If the whole key board was simulated you would have to put the ipad on something to be able to click like crazy and you would still have to look towards a down direction making your neck hurt.
But then again I find ipads as usefull as a cucumber with a tomato taste. If you really need to play all day long no matter where you are, you should buy a netbook, something portable, but a device that supports more stuff than watching a video and logging at facebook.
The other option is when someone leaves her/his house she/he should try beeing social and let the games home, where they belong.