I think ngc is posting here because he wants to see how the 40k vehicle kits stack up against historical models.
They are ultimately wargaming pieces, so they don't have the same delicate detailing that the best static display models have, because they are being literally manhandled by the gamers possibly every weekend or even multiple times a week. Add to this the fact that the average 40k gamer is a teenager and you've got a strong need to keep the model sturdy.
All this means that the 40k kits are a lot blockier and thicker in appearance than actual vehicles. Another influence is the cartoony nature of the imagery in 40k and the vehicles really look worlds apart.
That said, for what they are I think the 40k vehicles are fun build-ups and attractive kits. The molding and detialing have also gotten much, much better. The kits often come these days with a large sprue of optional vehicle add-ons and the crewed vehicles (things not possessed by daemons or anything
) come with basic but fairly attractive interiors.
So if you can get past the fact that the design sensibility of many of the vehicles is dubious at best, modelling the 40k tanks and walkers can be quite fun.
It is true, however, that they are outrageously expensive. This is mostly due to what the market can bear -- the average consumer of this stuff is not paying for it himself, he's getting mom and dad to pay for it. So the payor is not the user, and doesn't have a good feel for what a reasonable price is. Mom and dad hear that young Timmy wants this tank thing and it costs $50. They may roll their eyes, but what they don't know is that a bigger and much more elaborate Tamiya vehicle can be gotten for the same price -- or even cheaper.
It's like restaurants that get most of their consumers on expense accounts. Naturally they charge more that restaturants in which the consumer is also the payor.
To be fair, it's also true that the 40k gamer gets more out of his kit than the average modeler -- he uses it as a gaming piece. So it's more of an investment. Of course, it's up for grabs whether the modeler gets less out of looking at his build-ups than the gamer does using them in games every week.