I'm going to stick my neck out here and say
"STOP DOING THAT! YOU'RE WRONG!"
The protocol part of the schema is for the protocol, ffs. I don't actually care whether the .ics file you're serving me comes via HTTP, FTP or Gopher but I at least need to know what protocol to use. You might argue that I should default to HTTP but it's not exactly a huge stretch to imagine that, one day, HTTP might be replaced as the great circle of life continues. Hakuna Matata. Especially if we start having more mobile orientated protocols.
If only we had some way of saying what type the file was. Oh wait! We ALREADY FUCKING DO. It's called MIME types and they work just fine, thank you very much.
There are two objections to MIME types as far as I can tell:
- It's hard to configure handlers for them
I concede this may be true but a) that's a UI problem, not a protocol problem and b) it's no more difficult than having to configure a handler for a new pseudo protocol, especially since most browsers don't have UIs to configure protocol handlers and even if they did now we have to have two (2) different UIs (or one confusing UI) to handle MIME type and protocol handler set up).[*].
- Configuring MIME types is a server problem and sometimes I don't have access to my server config or don't know how to set things up. Waaah waaah waaah.
I concede that this would be a problem IF THE HTML 4.0 SPECIFICATION WHICH HAS BEEN AROUND SINCE 1998 DIDN'T HAVE A WAY TO SPECIFY THEM IN THE HTML
That's not to say that there isn't room for improvement - for example you can't paste a link into an email and then specify the mime type (although perhaps some pseudo protocol like http+text/calendar:// ought to be defined) however that said I wish people would stick to the standards - they're there for a reason and "because the URLs look prettier this way" isn't a valid reason to ignore them.
(I am fully expecting now someone to come and point out that this is all allowed under some RFC and that I'm wrong in which case I will concede gracefully and commit seppuku)
[*]Although I'm aware that browser have ways of configuring what mail client to use with mail://