Apple's thinking is presumably that they'd like to keep direct syncing with their OS for their own own iPhones, but the lack of iSync will prove a bit deterrent to those Mac owners on Leopard (OS X 10.5) and Snow Leopard (OS X 10.6) who were thinking of upgrading to Lion (OS X 10.7) - iSync has been the singlemost reliable sync solution I've ever used for my Nokia and Symbian smartphones.
Perhaps happily, there's an unofficial workaround. Apparently, if you have a Time Machine (or similar) backup, you can copy the iSync v3.1.2 application from a Snow Leopard backup to the 'Applications' folder in Lion and use it just as you used to - in other words, treating iSync like just another application, even though it's not part of the OS anymore.
Me? I'd heard negatives about Lion, with the change of UI scrolling protocols and some app incompatibilities, but the lack of iSync is the last straw and I for one won't be upgrading from Snow Leopard anytime soon.
Hopefully Apple can release iSync as an official OS X add-on/download.