Apple refuses to investigate and give a clear answer on this in public. They tried to ignore all evidences or analysis which shows it is a problem caused by its software. They blamed this problem to customer's defective hardware without evidence. It is obvious against the law. We need US government's attention!!!!
Reference sites:
http://iphone4s-wifi-victims.blogspot.tw/2013/10/apple-iphone-4s-wifi-er...
https://discussions.apple.com/message/23856966?ac_cid=tw123456#23856966
http://www.mactrast.com/2013/10/ios-7-causing-wi-fi-issues-iphone-4s-own...
http://appleinsider.com/articles/13/10/10/ios-7-update-brings-more-wi-fi...