That's right. Serial ports are an option though. You can custom order one with a serial port for use in a POS setting. Many retail businesses use these so that is a port that they must have for a business.
Serial Ports are legacy ports that just won't go away on PCs. Similar to VGA. The manufacturers keep them alive for backward compatibility with other devices. Businesses and large corporations are the main reason they aren't phased out. If a huge corporation has tens of thousands of monitors with VGA inputs only, how can Dell or HP sell them a PC that doesn't have a VGA output ? The expense to replace all those monitors would be enormous. The 3.5mm headphone jack is the oldest legacy port in history. Apple has tried to kill it but it's still everywhere.