"What terminal clients can't you use on RISC OS?"
Most important certain propriatary terminal clients which play macro's and a web browser which can be used to configure web page controlled applications. (and X, VNC, SSH but they might exist)
"However, the need to read MS Office documents and browse the web properly is hardly a downfall of RISC OS itself"
I didn't say RISC OS sucks, I'm a RISC OS fan myself. I just said I can't use it for most of the stuff I do in my daily life. You are right, it's not the OS itself but the lack of (good) applications.
In MS windows "there is no easy way to remove dead entries" but you can just leave them there, they break nothing. You can also just move application directories under ms windows as long as you update the shortcuts afterwards or click directly on the right executable to start the program.
MS windows doesn't get 100% out of the computer (not even close) and it's impossible to have 100% control about everything it does but it does have all the applications and is easy to use (if you exept you don't get 100%)