Go ahead and write to the memory, you wont be able to address it so it is pointless. Just because you can compile a program on a machine doesn't mean you can access a device without root access.
So you're telling me that I can't intentionally write beyond my own memory pointers in C++ on a VPM? Nonsense.
The physical machine is shared. It is only a PROGRAM on the OS that makes it appear to be separate machines to the various users. The root user sees the whole REAL directory structure. So the barrier between accounts is only as solid as the program controlling the access. Show me an OS that is without bugs...
I ran a webhosting company for a number of years, using Ensim at the time. Another problem that is inherent to shared machines is the tendency of the OS to remain outdated well beyond what you'd settle for if you were the only person on the machine. In other words, providers don't generally do a great job of keeping the OS as up to date as they should. The techs in those centers have an install disk that simply doesn't get updated as fast as updates are available.