Not true. Even on the PC side, people who have Xeon Workstation machines (such as HP workstations) rarely play games. Workstation motherboards usually have slow PCIe slots and slower RAM, compared to "consumer" Core 2 Duo lines.
I think gamers care primarily about 2 things...the performance (tweakable performance) and the price to get it. Not reliability, not server-style functionality. And though workstations have more reliability and less performance in one area, such as lower latency RAM, they compensate in others like FSB speed and on-die cache (a'la Zeon). Add big video pipelines, drop the price and make your guts swappable, and you've added "gamer" to your worstation vocab. Check out the results gamers are having at sites like http://www.firingsquad.com/hardware/ultimate_workstation_ultimate_gaming_pc/page16.asp . Or compare an Asus "worstation" board to a "gamer" board. Nowadays workstation hardware performs comparably to gamer, but the extra reliability costs more.
I prove it to myself when I compare a weaker card in my Pro vs a high end card in my PC and the Pro smokes it. The Pro is no simple workstation...it's a gamer rig in stealth mode, slowly converting everyone to Apple. I hope Apple stays on this line for a while.