Why is the federal gov. enforcing a conversion (U.S.) for all television signals to turn from analog to digital? Is there economic sense?
From the viewpoint of the electronics manufacturers, it makes all sorts of sense. They get to sell everyone a new TV with a digital tuner, or a “converter box” (actually an ATSC digital tuner with analogue outputs for use with your old TV).
Digital broadcast has significant bandwidth savings, allowing things like multiple audio and caption tracks. After the switch, the FCC will auction off the portion of the UHF channels 52-70, which will no longer be needed. This bandwidth can be used by all sorts of fun new technology (I have no idea what.)
Pffft. Most people have cable or satellite, anyway. The network feeds are handled by the system operators and modulated for the equipment on the network. The only people who need new TVs or converters are those who receive over-the-air broadcasts exclusively.
ETA: And it turns out the gummint will give away $890 million to subsidize the purchase of converters for households who receive broadcast signals only. I am confident that the federal bureaucracy will manage these funds with all due discretion and efficiency. ( 
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From http://www.dtv.gov/consumercorner.html#faq2
Why are we switching to DTV?
An important benefit of the switch to all-digital broadcasting is that it will free up parts of the valuable broadcast spectrum for public safety communications (such as police, fire departments, and rescue squads). Also, some of the spectrum will be auctioned to companies that will be able to provide consumers with more advanced wireless services (such as wireless broadband).
Consumers also benefit because digital broadcasting allows stations to offer improved picture and sound quality, and digital is much more efficient than analog. For example, rather than being limited to providing one analog program, a broadcaster is able to offer a super sharp “high definition” (HD) digital program or multiple “standard definition” (SD) digital programs simultaneously through a process called “multicasting.” Multicasting allows broadcast stations to offer several channels of digital programming at the same time, using the same amount of spectrum required for one analog program. So, for example, while a station broadcasting in analog on channel 7 is only able to offer viewers one program, a station broadcasting in digital on channel 7 can offer viewers one digital program on channel 7-1, a second digital program on channel 7-2, a third digital program on channel 7-3, and so on. This means more programming choices for viewers. Further, DTV can provide interactive video and data services that are not possible with analog technology.
Yes, I learned this when I bought a new TV recently. I had to wait until I had satellite hooked up and I figured out what DTV is all about. I was thoroughly impressed! NBC had three channels. Some weird 24 hours news that wasn’t MSNBC and I forgot what the other NBC was. Fox had the same.
Picture quality was perfect. Even for channels that were a little fuzzy on the analog side, in Digital they were perfect. Then there’s program guide information. That’s a plus. I was a bit skeptical beforehand, but now I’m very supportive. It’s quite a neat thing to get so many options over the air for free. If I weren’t on a contract for this satellite I would certainly get rid of it until my shows on cable came back. I simply don’t watch TV anymore, but it’s nice to have a few things.
The only real disadvantage will be to cable or satellite non-subscribers who live a long distance away from the TV transmitter. Analog TV transmission tends to fade with distance, giving a bad but still watchable picture out on the fringe. Digital TV transmission tends to be “all or nothing” so you’ll eiother have a greater picture, or none at all.
If you’re in that situation, you’ll need an outside antenna with a signal amplifier.
Personally, I’m getting a fantastic picture with an indoor antenna.
Or urban areas with crappy broadcast infrastructure, such as seems to be the case in the entire San Francisco Bay area. I moved here in 1987 and had to get cable to get decent reception of more than 2 channels, even though I lived in the center of the San Jose metro area, with enough high hills around this extensive flat urban area to put a plethora of impressive antennas. I expect to receive OTA ATSC when pigs grow wings; in the mean time I’ll get HD via satellite.