I'll add another thing to the think about - economies of scale. Snap On, Matco, Mac and Cornwell make certain tools that you can only get from them. By that I mean that those companies make certain specialty tools that aren't available from other outlets. Some of those specialty tools aren't sold in large quantities, after all if you're a GM tech and work almost exclusively on GM, you probably aren't going to have a lot of the tools that are specially made to make working on certain parts of Chryslers easier. When anything is produced in smaller quantity, the costs for research and development, tooling to produce the tools, setup time, etc. must be spread across a smaller number of items which means a higher unit price. So those specialty tools are bound to be expensive, but in all probability part of the cost for producing those specialty tools is also absorbed in the cost of the regular tools as well. When a company can get you to buy their specialty product that they make very little profit on and you like it, and it makes you money, then you're more likely to purchase more of their products which carry higher profit margins.
Add to this the things that have already been mentioned, such as excellent quality and fit and finish, tool truck delivery, etc. Another biggie that's been mentioned is the cost of financing right into the tool.
In the end, even though I rarely NEED a top notch tool like a Snap On or Matco, I take great pride in owning some of them and that makes them worth it to me. I don't have to drive around in a truck that's only a couple of years old because I buy a new one every four years, in fact it's not a good investment to do so. However, I enjoy the luxury and can afford the luxury of doing so and therefore I can value the higher cost. I consider my desire to add more top tier tools to my collection in the same light.
Do the trucks have deals that aren't on line?