Hmmm...except on guest O/Ss that don't provide RDP servers - like Linux, anything Windows version before XP and 2000 Server, NetWare, Solaris, FreeBSD, NetBSD, OpenBSD, etc. Sure, if you're accessing Windows Server or XP and later, RDP works fine. Also, RDP is only good after the O/S is booted - during boot you have no access to the console. This is fine as long as the O/S boots correctly, but if you have any problems with Windows booting then you may need something else.
As far as performance, RDP definitely has better built-in encryption and compression (VNC doesn't have any), but as long as you're on a 100Mbit+ network, VNC works fine.