I don't know about Revit, but Inventor and Solidworks are WIN32 API right to their very core. Basically everything in them is available on the COM interface as objects, which is awesome for writing extensions to the programs on Windows. I suspect the trade off is that they are so all-in on WIN32, that they just touch way more of the API than games do, so they probably expose much more of missing API. They both rely on Microsoft Office for a variety of functionality, particularly Excel to manage tables of data. They rely on SQL server for the Vault and PDM products. They are Windows based through-and-through.
