Different versions of Mac OS X contains different versions and family of CCID driver.
Contains the ifd-CCID driver from Jean-Luc Giraud. This CCID driver is limited and has not evolved since its inclusion in Mac OS X. This driver does not support T=1 cards withe a TPDU reader for example.
Leopard also contained the same ifd-CCID driver in the first 10.5.x versions.
Then Apple replaced it by my libccid driver in 10.5.6 using version 1.3.8 of the driver.
Snow Leopard (10.6)
Since Leopard 10.5.6 the same 1.3.8 driver is provided.
The CCID driver binary is still a Universal PowerPC and i386 binary even if Snow Leopard does not support Power PC and the PC/SC framework is 32 and 64-bits. It looks like the CCID driver has not been recompiled for Snow Leopard.
Rumors says that Apple may update the PC/SC layer in a future version of Mac OS X.