Web requests made from UIWebView will not include the word “Safari” in the User Agent string. Web requests made from Mobile Safari will. This is the best way I have found for determining of a request is coming from within an app or from Mobile Safari.
Sample User Agent from UIWebView within App:
User-Agent: Mozilla/5.0 (iPad; U; CPU OS 4_3_2 like Mac OS X; en-us) AppleWebKit/533.17.9 (KHTML, like Gecko) Mobile
Sample User Agent from Mobile Safari:
User-Agent: Mozilla/5.0 (iPad; U; CPU OS 4_3_2 like Mac OS X; en-us) AppleWebKit/533.17.9 (KHTML, like Gecko) Version/5.0.2 Mobile/8H7 Safari