Well, in defense...I noticed web design and development was not on the list so maybe the question was concerning web graphics specifically since design for the web has different requirements than print graphics. Like how file size is a big limitation for online graphics but doesn't make any different for print....web graphics big advantage is the flexibility. They can be changed easliy,often with little expense and you are much less limited by color versus price.
Here's my try answering the first question...look for information on image optimization and vector graphics.