Content originally posted in LPCWare by Daniel Widyanto on Sun Sep 30 21:48:45 MST 2012
Let me clarify this.
If your MCU VDD is available, but MCU VDDIO is not available, then you will have problem with the USB_VBUS pin (actually it's more like all of GPIO pins, coz the diode on the pin will not be turned on). That's what the sentence actually imposed.
If you tied your MCU VDD to the VDDIO, and USB_VBUS pin, the condition where the MCU VDD is available but VDDIO is not available will never happen. So, it's perfectly safe to connect all of these 3-pins to the USB Vbus without additional components.
Of course, I always recommend additional ESD diodes on each of USB pins (Vbus, D-, D+, GND) for better protection. But it's up to user to add it or not.