The CPUs were powerful enough, sure. The GPUs (Intel GMA950) absolutely weren't. Even on Windows with better drivers, Half-Life 2 is a slideshow on that class of hardware.
E.x. notebookcheck indicates that FEAR (released a yearish later) could get 20-30ish FPS at 640x480 but chokes at 1024x768 (at numbers matching the HL2 lost coast demo slideshow at 1024x768).
Gotta remember a lot of mac people were just happy to play something more modern than Marathon or Giants CK
I got my gaming start on one such machine - the Mobility Radeon was fine for HL2/Portal at 1024x768. Good memories.