I think perhaps you're unfamiliar with the open source competition. Most of the open source VNC servers support something like H.264 which while a little dated, is still quite efficient, especially for the low-latency streaming needed for remote desktop applications.
The only novel-looking thing I see on RealVNC's website is adaptive bitrate, which I don't think I've seen in the open source servers.
You know, I might be. In that case, please enlighten me with a counterexample. Anyway, the point isn't to pick on the competition. I'm merely saying that RealVNC is a fine, fairly priced product with a rather bad name. Many people, myself included, have a dismissive initial reaction based on memories of old-fashioned (slow, hard to set up over the internet) VNC. At least with RealVNC, it's nothing like that anymore, whereas with TightVNC for one, it still pretty much is. I use the latter as well, but only for light usage on local networks—acceptable and better than it once used to be, yet a completely different experience.
The only novel-looking thing I see on RealVNC's website is adaptive bitrate, which I don't think I've seen in the open source servers.