It was removed for Vista, because it couldn't transition to AMD64. This was after Microsoft had essentially completely ditched Itanium.

(I'd love to see a GOG or Steam or even Origin release of Full Tilt Pinball, though. The Full Tilt version of Space Cadet is better-- higher-resolution graphics plus some gameplay tweaks.)

[edit] Digging a little deeper, that might not be entirely true. The first consumer version of Windows it didn't appear in was Vista, but it sounds like the decision to drop Pinball was made during the XP era (even though it shipped with x86 Windows XP). So issues with the IA64 port (or with another architecture) might've been the reason it was dropped, then that decision was not revisited for Vista even if Pinball might've worked under AMD64 Windows.