the fundamental unix philosophy of "everything is a file" allows for a fundamental blockade of all or any content for any user or user group, which makes it impossible for a virus to do anything devastating, even if it is run, unless the user also chooses to grant it admin rights.
in windoze the abstraction methods of the system vary, and so there is no fundamental method to block stuff, which leads to difficult to find security holes.
I don't see anything to suggest the fundamental architecture is less conductive to people giving admin rights to stuff they shouldn't than Windows.

(Other than the user-friendlyness of Linux not being attractive to those most likely to give admin rights to everything and anything)