But is selling a lot more product really anyone's goal, regardless of profit margin?? Would it be your goal?
If for example, by selling the DM42 on amazon, it cuts SM's profit in half, then they'd have to support twice as many customers for the same income. While there is little doubt some of those extra units could lead to other sales (friends or repeat business) you could not convince me it would more than make up for it, since those additional sales would likely also come via the lower margin channel.
I'm with Walter - I prefer 100% of my money goes to SM.
Also, I'm sure you could track history and verify that sales through other channels did not begin until well past the initial demand for the other models was satisfied, so these are truly incremental sales (likely to folks that were unaware of SM). So, maybe next year, or the year after, the DM42 will be available in such channels...