As to the US <G>....
In the enroute environment we have two ways of displaying weather. We have the NEXRAD which is a weather service doppler wx radar. The info from this radar takes between 4 and 10 minutes to update depending on what mode it is in, and the controller has NO idea of the mode it is in. We display three levels of weather. Basicly level three as moderate rain, and then level four and close to five as heavy rain, and then the third band is displaying the high end of level five and then level six. This is also called just heavy rain. We don't display the first two levels so as to keep out ground clutter on the display. This is both good and bad. Bad in that we don't see some of the earliest buildups as they are growing and especially in the middle US where we can go from a towering Cu to a full mature thunderstorm in about 10 minutes, we could be describing a nice area and be putting you into a level six and would never know it.
The second type of weather display is that of the OLD weather overlay that came from your primary radar. It was digitized and overlayed in lines for light weather and H's as heavy weather. It was not the most accurate in that our radar was designed to filter out weather so that we could see aircraft (primary returns). It also suffers from annonymous propegation (or however you spell that.) These days probably 99% of the controllers don't use the old stuff.
The new stuff is nice for a general idea on movement and how the stuff is working in a line. But for summer time stuff that just pops up and goes away it is pretty useless. Many controllers however forget that it is historical data.
The approach controls all have some sort of real time weather display. The old ASR 7 and 8 radars have just one level of display which is a blob of precip. It is very accurate, but you have no idea if it is level one or level six. The ASR 9 and 11 radars all are doppler and have a WSP that allows for weather processing. If these radars are being used at an approach control with the OLD monochrome radar display (they are going away) then they can see three levels of the six. Two are displayed and one is observed as a blank area. If these radars have the new STARS display or the new Color ARTS display, they will get to see a color six level weather display which is normally pretty accurate, and it is updated every six seconds. We still aren't supposed to vector around weather as we see it since we can't guarantee that is where it actually is at, but we can try to paint you a picture so that you can use your airborne equipment to figure out a good way around the stuff.
As to NEXRAD in the cockpit, there are a couple of ways of getting that data in the US with datalink to your cockpit display or even to a PDA. All you have to do is pay for it, the same goes for the airlines, you can get all the data that you want to pay for. The airlines these days are not paying for anything that they don't absolutely have to...
regards
Scott