I think (not 100%) that the online interface is more intuitive and user-friendly (and forms view would probably confuse a lot of users).
desktop has both interview mode like online and forms mode for those that know what they are doing. however, the amount of help in desktop varies with the version.
They've always been different, we don't really know why. The one time they tried making desktop more similar to online, it was by reducing the features of desktop, and the desktop users revolted. (I believe that desktop has more net profit than online because desktop users need less support, but that's just an impression I remember from a news story a long time ago. They probably make more gross income from online since there are so many extra cost add-ons.)