Other sims are also around and the weather needs to be mostly the same for all simmers - just like in real life - there is one true weather valid for all (if simulating reality) - it clearly makes sense to share the same weather (unless you choose not to fly real weather) - there is also another discussion about 3rd party access to the weather system. It will be interesting to see how this weather system will improve and how it will affect flying on online networks.