On my Arduino Uno R3 and Arduino Mega R3, there are 5V and 3.3V pins.
Why is there a discrepency?
The link you provide looks rather old and I don't think it applies to UNO Revision 3 as it has more pins than on the diagram you show.
I suggest you rather take a look at this Arduino UNO link which contains uptodate information about the UNO; in there you will see that for R3, the "power rail" has been extended and has the following pins, left to right:
There are three power supply pins on the Arduino Uno and on the Mega: