HAHAHA, I didn't say they where equal. Indeed Autocad 3d, Inventor, Solidworks, Rinho, 3D studio max all have there own application, and to get good modeling you really need to use a combination of each.
Google has one huge (in my view) advantage over the previous stated is that its free and also there is an open source element to the program that allows you to add extra drawing functions (ruby console) I have been using Google (free) for almost 3 years, you can create 3d curved profiles extremly quickly, it has 2d - 3d viewing with heaps of functions. - you cannot draw a ships hull in Inventor!
Its not the best for making manufacturing drawings, but again with a little work its not so difficult.
For home use and concept design its an amazing program.