So if you buy the programming kit with any of the languages, you'll be able to write, compile and download programs to the robot. I'm not sure what implied you wouldn't be able to do this. So rest assured, if you get the $100 kit that comes with 1 of the 3 languages, you'll be fine.
RobotC has the ability to write both the master code and the user code to the Vex, I believe it either comes with it or you download it from Vex's site (been a *long* times since I set it up). Hopefully I have those terms right
When you are writing a program in RobotC, you just do the "compile" and "download" buttons/menu/keyboard shortcut and you are good to go. I usually compile it as I write, to make sure I'm not forgetting ; and syntax stuff, then when I'm ready just "compile + download" and watch the debug output you get while connected to the bot.
Quite nice, I think.
The one thing lacking that I *think* EasyC has (and I could be totally wrong) is computer control of the robot via the serial cable. As in, there is no way to do using the computer itself what the controller does (4 analog channels, 2 "button (digital?)" channels).