The aussie government discussed this .. afaik (prove me wrong if you like) .. it was down voted .. invasion of privacy. I guess USA & UK govs do not understand or respect privacy. Exception is for Child pornography however in most countries in the world. Over here they will set the person up, not invade them without evidence. In general, the legal approach here is 'innocent until proven guilty'. Whereas I believe in USA 'you are guilty until proven innocent'.

Different countries have different requirements upon ISP's keeping history records (some governments require the ISP keeps records for a certain amount of time.) And also in part it's up to the specific ISP in some cases as to how long 'they' decide to keep records.