Pyjamas during the day are de rigueur here. It is common to see women going about their daily business wearing a two piece suit out of cotton or polyester (the shiney kind) finished with a pair of dainty sandles and a handbag.
Sometimes just the bottoms are worn. These long shorts are very common I've even seen men wear them.
I can't see myself wearing pyjamas to town but I understand the comfort factor. It is hot here and zips and flies, lycra and denim are not the most breathable fashion trends. Khmer women work often sitting down or squatting in a hot market for hours. An elastic waist and loose pants make life just that much easier.