That's the problem. While I enjoyed the movie, Downey wasn't playing Tony Stark-he was playing himself. Stark is not a smart alecky kind of guy; Downey is.He didn't even seem to be acting, just being himself.
That may be so, but with all due respect, the general audience couldn't care less if it is 100 percent faithful or not. All they knew was that they had an enjoyable two hours. Most people had no idea of who Iron Man was and all the intricacies of the character. This is Downey's interpretation, and it has done it's job by getting people into the cinema.