On either platform, some dialog boxes and menus can be captured, along with the cursor. There are many dialogs and menus that cannot be captured this way. Third party software is available for these images. They also have helpful features to control the size and file format of the captured image. When you save something you have a choice of formats.
Text is the one most used for saving web pages.
If you want to maintain the HTML code of a page you can save it as Source. In an e-mail message Source becomes more important. More on this below. You can click on the links to see what happens. Once in awhile you get the actual programming code.