This is not true. There are plenty of restrictions for foreigners travelling in Xinjiang, especially outside of the touristy areas in the main cities. Large areas are unreachable without special permits, allegedly due to "safety reasons".
http://oldroadtours.com/index.php/preparing-for-your-tour/vi...
Outside those it's mostly local gov/police not wanting foreigners walking around, not being allowed of the bus between the larger cities, them being sensitive when getting somewhat close to the border with Kazakhstan, and Bingtuan. Having "paperwork" is required then.
Plus, restrictions come and go on forcing foreigners to only travel with authorised tour agencies, or authorised guides, that won't take you to some places. And whose presence will make local people suspicious of talking to you.