TT makes a special PC version that is "amend only." Since they don't make a mac amend-only version, the customer has to get a fully functional Mac program, and that can't be posted as a free download for hopefully obvious reasons.
The reason they don't make a Mac amend-only version is probably limited demand--they save enough customer support telephone time by having a PC version to make it worth programming, but they must figure that having a mac amend-only version will not save them enough on tech support representative to be worth programming.
