This is one time where I believe Dilbert is wrong. The only way he might be justified is if the unnamed colleague is the ONLY recipient of Dilbert's email, or if Dilbert is VERY highly paid.
Because it is not the time of just one individual that is wasted trying to figure out the gist of the attachment, but of ALL the recipients. Although in this context the attachment presumably was germane to the present meeting, too often people send out messages with attachments that really don't need to be read. A single paragraph by the sender would be sufficient for 90% of the recipients, but the sender has no respect for them.
(Yeah, Scott touched a nerve here. And it's usually the PHB types who are to blame, not the Dilberts. But still, Dlibert's response is well-played, and the punch like gave me the usual laugh.)
I think you're missing the point. Dilbert showing the co-worker his pay stub says a number of things; the most obvious is stated in the final panel: "I brought my paystub to prove my time is worth more than yours." Other things it says are that the co-worker is out of line with his lame excuse for why he didn't prepare for their meeting and has nothing with him (obviously the least of which should be the document for discussion).
I think it also illustrates most peoples' desire to be seen as more important than we really are and in Dilbert's case, he was able to put this associate in his place. We've all worked with those people who are upwardly motivated but not upwardly mobile... we call them leeches. Kind of a psuedo-executive whose lips are permanently attached to the higher-up's bum. This leech happened to appear in a meeting without his host...
The preceding "chi of Dilbert" commentaries seem a bit over-analytical to me. What I see is this:
1) Lowly paid employee is a bottle neck for a process - and he knows it.
2) He compensates for low wage by trying to exercise control of process (what little he can control) and uses excuses as noted above - presenting the illusion of importance.
3) Dilbert anticipates and goes straight for the throat by crushing the lame excuse with facts.