It's a common security practice to not show guests the exact versions of software you're using. The reason is if there's a security update, you won't be advertising to the world that you're still using old/insecure software. (you could Google old version strings to find vulnerable websites, etc)
I'm still new to WebCalendar, so forgive me if I'm missing something, but I noticed that it shows its version by default.. is there a real reason to do this? It would be nice if there was a way to turn it off without modding login-app.php and other files. I am happy to link to the WebCalendar website, I just don't want everyone knowing exactly what application versions I'm using because.. these threats are real.