Yes, you can buy a cloud offering, but physical disk is still way cheaper than "cloud disk". You don't have all the cloud features, but on the other hand, the data are 100% yours, on a server that you control.
I've been trying to actively discourage the use of FTP for the last 10+ years. It's not an option because it passes passwords in-the-clear. Protocols that pass cleartext authentication should just be off the table today.
The number of times I have had to correct tech-ish friends when they talk about "telnet-ing" into servers is frightening. All of them were relatively technology literate but either didn't do it for a living or got into doing it for a living "by accident". Think your physics major buddy who has only ever used windows on any computer that he owns.
You put people like that in the position to make a call, and I assure you you'll have an FTP server running somewhere in 5 minutes flat.
It's also the case that SFTP requires giving someone an actual user account on your UNIX box, and preferably knowing enough about how to set SSH up to restrict them to SFTP access only. If your server is much more valuable than the data and you don't trust yourself not to get SSH configuration subtly wrong, it's not terribly unreasonable to prefer installing an FTP server to adding a local user and giving someone else a password to it.
If Microsoft every had of built a decent client into Windows Explorer like MacOSX has (rather than the crufty, half baked one they ran with) then it could have been great. As it turns out, it is only really easy to access it through FTP-like programs (separate from Windows Explorer).
Having said that, we had pretty good experiences with WebDrive  allowing us to mount WebDAV directories in Windows. Also, Gnome does a pretty good job on Linux with GVFS .