YES!
No one, except Microsoft, would create an operating system (OS) that the last several generations of computer couldn't run. All G5 systems will take full advantage of Tiger, All G4 systems will take advantage of everything except Quartz Extreme (for those with small VRAM), or 64-bit memory addressing. G3s have the same disadvantages as G4s, plus Tiger will only run on those G3s with built in USB ports (and I assume firewire [to drop many of the early iMacs]).
Pleas stop asking these mundane questions, Tiger will not make all the Macs out there obsolete, in fact, most older systems will run faster than with Panther.
TEG