For a cartoon this is funny; Sure.
In real life: People who send huge attachments instead of summarizing the impotant parts are idiots.
Explanation; It's extremely common that the person who intends to share a certain information already is ,well. familiar with the topic, The person who receives it isn't (this is generally what causes the need for the information to be shared to begin with). The person who is conveying the data is usually just talking about a fraction of the data within a document. Not to mention the fact that the person who sends the data know who he sends the data to, and can adjust focus and terminology for the specific recipiant and usage intended. The sum of this is that the time used for the person conveying the message to summarize the important parts in to his own text is minute compared to the time the recipiant would need to evaluate the document in full form to find the fractions of relevant data he really needed.
For good communications attachments should only be used for forms, and to keep a link to original data, in case the recipiant wants to check the references used, not for the message in it self.
The "too busy to read your attachment people" are wonderfully fun. If they ask questions that are answered in the document, I answer yes or no. Then ask for their opinion about something in the document and CC: everyone. Those that read the document know what I'm talking about and the rest will probably never know. They either read the document or ask more questions proving they an idiot.