This is an interesting idea, and actually quite clever. The adventures create the market for the miniatures and therefore ensure interest. I can think of a couple of complications though:
1) Co-ordinating the artists who work on the adventure with the miniature sculptor might be fiddly and time-consuming;
2) Seeing the miniatures would ruin the surprise for some people. Unless they were hidden from the view of the players, behind a spoiler warning in the online store or something, but third-party stores probably wouldn't co-operate. And not being able to show the miniatures to the players would offset the value of using them to sell the adventure.
It's a great idea though. I would totally buy minis specifically for adventures. In fact, I have a hard time finding minis that are suitable for adventures I run in the first place, so something like this would be a godsend provided the minis match my mental image (or the illustrations, whichever is more powerful). The above issues would have to be worked around though.
Hey, how about mail order? Buy the adventure, get a coupon for a special one-off mail-order mini. This could be done every time an adventure is released.