The reality is like Reinholt had said is that GW prices are resistant to price change. What this means is that instead of a strait line when you graph Price vs. Demand it has more of a curve(closely represented by y=Log(-x) for you math folks). For those who aren't familiar with logarithmic curves, think of a cliff except the edge is rounded. Now for the most part a price rise won't effect the demand much if at all... Until it hits a breaking point where the price just start getting too high for more and more people and then it hits the true cliff where it demand plummets. The reason why the curve is that sharp comes to the critical mass point that Reinholt stated as well, getting people to try other games was difficult because most people didn't want to risk outlaying money from a game system that they were almost guaranteed to get a game in as opposed to one that there may only be one or two other players. Now we are seeing the cost to try other games be cheaper then a new unit in your old army, It's not that big of a risk anymore then buying a new unit and finding out you don't like it and because of that now, other game systems have enough people to play that you don't have that barrier of entry of "no one to play".
Now IMO we are in the fast transitioning part of the curve, I think we are just starting in it, and we'll really see the big drop off of demand come after the next two year's price increases.
If you need the logical reason why the OP theory doesn't work think of this: Once GW makes enough Land Raiders to cover the people willing to buy it at the current price whether they produce an extra 20 or 20,000 makes no difference. If they fail to produce enough to meet demand do you think that it is going to make that model worth more, not likely. Sure GW could try to make them ultra rare (like forgeworld used to be) and only make 250 each year for the entire world but even then its unlikely that people would want them anymore. I mean look a 3rd Ed. Space Hulk the price for that on ebay has been going down for a while because once they got out of speculators hands even though they are relatively rare to find up, not many people are really interested in them that don't already have them.