Any application, not just GNOME applications, can use filesystems mounted with GNOME's 'connect to server' feature, for instance. I think it's more desirable to write a FUSE module than a KDE-specific KIOSlave.
You say that, but if you look at the apps on the ground, most, well, don't. For instance, I can mount my network drive using GVFS all I want, but I still can't watch anything on it, since VLC has no clue about it. A nice idea, but it would be preferable if they integrated it into the rest of Linux too. That said, I use Gnome every day.
No man is an island if he's on at least one mailing list.