Whiskey in US movies out of plain glass decanters. A movie or culture thing?

This isn't just a US thing, I think this was originally British.

When I was growing up serving guests liquor from decanters (the fancier crystal glass the better) was seen as classy, and serving from a labelled bottle was seen as a little crass. Another one of those creepy little British class system things old money folks use to spot new money folks.

I think it's also something to do with trusting your host's taste.

It doesn't just apply to whiskey - just about any strong liquor would have been decanted in this way.

I think anyone attempting to appropriate British style upper class mannerisms would do it, so it's appropriate for both 50/60's ad execs and modern politicians to affect it too.

Decanting was originally used in Europe for drinks that might contain sediment (port, sherry) or wines which need to "breathe/oxidise" for a couple of hours before serving. Decanting for your guests was seen as being hospitable.

In more modern times, in the US the 4 largest tobacco companies signed up to the 1998 Master Settlement Agreement to avoid law suits and liabilities related to medical problems attributed to tobacco use. Under the agreement the companies are required to annually compensate 46 states for medical costs related to tobacco use. They also agreed to abandon many marketing practices including marketing to teens. They agreed to pay a minimum of $206 billion over the first 25 years.

To avoid similar liability issues and law suits around alcohol placement, the drinks industry has introduced self-regulation, but its not rigorously followed (eg. Ted, The hangover, 21 jump street etc)

My understanding is that currently the guidelines state, if an alcohol brand is promoted by a movie, at least 70% of the audience must be of legal drinking age, nobody in the film under 25 should be involved (drink/make) with the alcohol and the film should only promote responsible drinking (no drunken car chases, binge drinking etc)

Liquor advertising is legal in the U.S., but it is a contentious issue. It is pretty much guaranteed that if distilleries advertise too much in the wrong markets (i.e., much of the audience is under age 21) laws will be enacted probably to completely ban such advertising. Currently industry trade groups create and enforce the standards.

A show like House of Cards probably doesn't appeal to minors in any great measure, so showing a whiskey label would not present any problem.

However, should the series be shown on a television network, it could provide a issue. That and all the cigarette smoking.

However, using an anonymized container is something that many older people in my family did when entertaining at least in the 1960s through 1990s. Grandma once said it was to help keep the conversation on the people and not about the drink.

It seems realistic to me in Mad Men. I am sure they are (portraying the) drinking (of) top shelf stuff. And it looks nicer that way too.

I don't think anyone would mix it. But maybe vary the brand without calling notice to a change.

I believe the primary reason is to avoid the licensing and legal issues that would arise from using an actual branded alcohol.

There are the legal issues, but, often, the best spirits or fortified wines are from older vintages, especially with a vintage port. Original containers can get a bit dirty and dingy with time.

Quite often, with a vintage port, the bottles are so old that you can't get the cork out of the bottle without it disintegrating and getting pieces of cork in the port. Also, with something like that, you get quite a bit of settling of particles and sediments that get stirred up if you are picking up, tipping, pouring and putting bottles back down, repeatedly.

To properly open a bottle of vintage port, you take heated tongs, and grasp the upper part of the neck of the bottle with the hot tongs. Then you take a cloth that is whetted with cold water and wipe the hot neck of the bottle. The sudden thermal contraction causes the neck of the bottle to crack, cleanly, allowing the top to be removed with cork intact. You'll want to decant the port from your intentionally broken bottle, that you can't re-close. Generally, when I see that in movies, the drinks are in a fancy crystal bottle and serving set.

Just some trivial facts to add to the bigger picture laid out by other answerers.