It's called professional courtesy.
Anyone who releases software for commercial purposes understands that the only constant is change. If you have a multiplayer option and allow folks to connect up, you understand that you will never have 100% up time. Hell, even MMORPGs like World of Warcraft, with millions and millions of users still can't guarantee 100% up time.
So, since many of the same developers are just local peons like us as well, one would think they would provide "some" ability so users can still enjoy the game, with friends, even if their servers go down.
I can't recall the last time I had to pay a monthly fee to connect up to multiplayer Realflight, so why the strangle hold on multiplayer is confusing as best. Just because multiplayer isn't "Guaranteed" does not excuse them from at least providing an option to users to connect up independent of their servers.
<EDIT>
You can play Realflight multiplayer across the internet, however, you need to set up a Hamachi(now called LogMeIn Hamamchi) VPN service on each person who wants to join in. Hamachi allows up to 5 users for their free service. It costs about 30 bucks a year for a 32 member option. Hamachi creates a LAN across the internet to connected computers, so Realflight sees it like a LAN game. Downside, everyone who wants in has to install the Hamachi client, and by doing so, opens up their computer to everyone else on the VPN. Creates a serious computer risk to the folks who might not be as tech savvy.