Buying prepaid SIM card requires ID?

A couple months ago I was able to easily buy China Unicom prepaid SIM card at convenience store in Shanghai without any ID. I am in Guangzhou now and when I go to 7-11 to buy prepaid SIM card, they ask me to go to the China Unicom store. I tried buying from street vendors but they all asked for an ID. Is it common practice everywhere in China or it is just Guangzhou tightening security ahead of Canton Fair?