2donkeys
Sorry I'm not familiar with the US NEXRAD system. However your question about uplinking weather to aircraft via datalink is a good one. Why don't the airlines do that?
As to the differences of UK versus USA, well the systems (apart from NAS) are different, hence the need to develop from the ground up in UK. Although there is a European attempt in progress to give a common ATC system (SACTA), delivering to NERL in the CASPIAN project, hopefully rolling out in 2011/12.
No intention to re-invent the wheel as NERL will look at other places which currently have that type of info displayed as a part of the study.
BTW to those who mentioned tinting the radar display for weather. How does that affect the quality of the picture and (more importantly) the clarity/viewability of the other colours on the screen? We have a lot of issues with viewing quality, font size etc. etc. and that sounds like a recipe to exacerbate them!
BD