As long as we're on the topic, I use Command-Shift-4 (and -3) a lot, but I changed the default file type from png to jpg, with this command in Terminal: defaults write com.apple.screencapture type jpg
I find jpg to be handier, but it's not for everybody.
You could use Command-Shift-4 and then drag to select the portion of the webpage. That'll save a graphic file on your Desktop. Then, double-click that file to open it in Preview, and print from there.
Another option is to use
Grab (it's in your Applications > Utilities folder) to capture the portion of the screen you want & then Print it. Grab can also Save the image as a TIFF file.
The
Command-Shift-4 procedure saves the selection as a PNG image. You then have to open the image in Preview and print from there.
The best little gadget for this is Printliminator, which is a little Javascript bookmarklet that allows you to select a portion of the page and erase it from the page, or erase everything else from the page.