Hi Byrna,
Sorry about the delay, I was away.
Anyway, the Jeppesen weather you can download from FS is real and up to date aswell, in fact, weather generation is a vast improvment on FS2002(I think this was one of the big selling points). However, programs like FSMeteo etc.. make weather generation more configurable eg.. You can set up destination weather and get the program to lock to this when you reach a certain distance to your destination. This stops the weather from up dating to a nearby field when you're about 5-10mins from touch down.
Active sky has a processing system, were it downloads surrounding airfields aswell and plots weather transitions, so the weather won't abruptly change. You can see a cloud layer approaching rather than suddenly popping up and see different weather systems in the area of an airfield. AS also has a working weather radar!
With FSMeteo(Not sure about AS) you can also enter in your flightplan and it will download the weather points on the route and show you the best route/altitude for winds ALOFT, very handy when you're on a long haul.
Both are excellent programs. AS is quite advanced with a lot of extra features(Weather radar etc..) and can use a lot of processing power, whereas, FSMeteo is a much more basic program(It just makes the weather) and won't eat into frame rates as much.
Anyway, hope this helps.
Cheers!
PS...Mods, apologies about thread drift.