There have been discussions in several recent threads on this very topic. The basic problems are as follows (not in any specific order):
1. Too many Americans have the "WalMart mentality" and want everything as cheap as they can get it. They do not understand the true value of things. So companies who can produce this technology are not interested in selling it in the USA. They would rather sell in Europe and Japan where they can make a profit. The SD DVR I bought 2 years ago with no monthly fees cost me $600 (which is at a discount).
2. TV-Guide/Gemstar has a stranglehold on "guide data" in the USA. So the choices are; a) pay TiVo, b) pay cable/DSS, c) buy a product with no guide at all, d) buy a more expensive product (see 1 above) with guide licensing built in. While us techies have no problems with programming VCRs and setting timer recordings on computers & DVRs, most of the population apparently does. The on-screen guide and user friendly GUIs of modern DVRs has solved the problem .. for a price.
3. The broadcasters don't like the fact that we can use DVRs to totally avoid commercials. They are even willing to "give" us a free DVR which has the FF functions (at least during commercials) disabled. TiVo, cable & DSS all have "broadcast interests".
4. TiVo, charging upwards of $20 per month for their guide (data), has not made a profit in years. At $200 they do not break even when they "sell" hardware. It costs quite a bit to run a service providing daily guide data to all their users.