I'm with the OP here. I purchased an iPad for my 5 year old son with autism. I have downloaded a number of fantastic programs, including "Proloquo2go" which is the app which convinced my wife and I to buy the iPad in the first place. My son has a fabulous vocabulary for his age but he is entirely non-verbal. The app is amazing but the keyboard is way too sensitive for my son who has no difficulty using a hard keyboard. He is constantly hitting keys by accident and this causes even more frustration for him. A sensitivity setting would be amazing and should really be implemented by Apple ASAP.
I have emailed the developer of "Proloquo2go" hoping that they will release an update which uses the API for keyboard sensitivity and am awaiting a response.
In the interim, though, please keep in mind that there are many users of this technology and those who don't see this as a problem, great for you, but don't assume that your experience is universal for all users out there.