I think $150 is more expensive than what I was expecting. But I don't think it is tremendously unreasonable and I already KNOW I will spend that money. It should be noted, of course, that my entertainment budget is fairly large. I am a forty-something married father of two teenagers. I am lucky enough to make a decent-enough salary that my wife was able to stop working to raise our kids and we are able to indulge our various hobbies (of which gaming is one). Most of my players are my age and similarly comfortable. Obviously, this is not the case for everyone.
But the reason that the value proposition used to evaluate D&D are leisure time activities like movie-going, dining out and other such activities is that they are in the same immediate cost level but often have a radically different value proposition. This past weekend my wife, son and I went to see Godzilla 3D at the local IMAX theater. These tickets cost ~$60. We normally would not spend that much on movies, but felt this was a special occasion and it was worth the price. The movie is about two hours long: so per person that was about $10/hour of entertainment. In terms of value efficiency, not so great. A few weeks ago, my wife took me out to see Eddie Izzard in concert in the city. She took a train in (so we didn't pay parking fees) for about $8. We went out to dinner for $40, picked up our tickets (~$70, iirc) and then went out for desert after ($20). It was a great date night, a rare one time thing. It also worked out to about $20+/hour per person in entertainment value. And we thought it money well spent.
Obviously, there are far better value propositions. Staying at home and watching Netflix? Let's see that's $8/month, so a four-hour night in is pennies on the dollar. Of course, that's because we've already sunk costs in the TV, the cable, the Internet, the living room furniture and all the rest. When I play Assassin's Creed IV, technically I'm getting something like 40-60 hours of enjoyment for $60. But that's again based on the fact that I already have an Xbox 360, TV and so on. In light of the amount of money I've spent on D&D versus the hours I've played it, D&D comes out as a fantastic value: 3E cost me $80 for the core books ($20, $30, $30 in 2000) and resulted in hundreds of hours of gameplay, enjoyable online time (in places like this) and social add-ons, including making friends.
So the reason that D&D is brought up in those terms, is because often its meant to highlight the fact that people don't always make that connection. People who wouldn't think twice about paying $5 for a latte, $10 for a pack of cigarettes or $20 for a case of beer balk at spending $50 for a D&D book. That's not an invalid decision, but some people are blind to the money they spend and where they spend it. There is no right answer there, since there's more to the value of entertainment than fun/hr, nor is it a mutually exclusive equation. But it's a valid argument that people undervalue D&D's returns on fun versus the cost of the books, IMHO, and one that should be pointed out.
As for why people don't bring up other RPGs? Well, speaking for me: because they're not the 800 lb. gorilla in the space. They don't have the market presence or the fanbases that D&D has. The benefit of Dread being contained in one book is nice, but it's not the same thing as going to a convention and finding thirty D&D games going on and one Dread game. It's likely the only way you'll play Dread at your FLGS is if you run it, but D&D I have a pretty darned good chance of playing nationally. Those games are great, but Spirit of the Century can't AFFORD to split into multiple books. That's why The Burning Wheel comes with two books that you need to buy at one time. They wouldn't be able to make enough money to justify the printing costs otherwise.
