I guess this is a side effect of apple's triple-platform-safari strategy. Apple apparently needs to put more effort into safari's security.
http://www.engadget.com/2007/07/23/safari-exploit-gives-hackers-full-control-of-your-iphone/
http://www.engadget.com/2007/07/23/safari-exploit-gives-hackers-full-control-of-your-iphone/