Agreed. But how does that apply here, really? The system monitor is not installed by default and is not needed to use the system GNOME is offering. The case here is more alike if Ubuntu bundled some vim plugin into their default installation and people throwed shit at vim because the plugin doesn't work.
Look at the scenario from the customer's standpoint. You bought programs X, Y and Z. You then upgraded to Windows XP. Your computer now crashes randomly, and program Z doesn't work at all. You're going to tell your friends, "Don't upgrade to Windows XP. It crashes randomly, and it's not compatible with program Z." Are you going to debug your system to determine that program X is causing the crashes, and that program Z doesn't work because it is using undocumented window messages? Of course not. You're going to return the Windows XP box for a refund. (You bought programs X, Y, and Z some months ago. The 30-day return policy no longer applies to them. The only thing you can return is Windows XP.)
This is just the tip of the iceberg with respect to application compatibility. I could probably write for months solely about bad things apps do and what we had to do to get them to work again (often in spite of themselves). Which is why I get particularly furious when people accuse Microsoft of maliciously breaking applications during OS upgrades. If any application failed to run on Windows 95, I took it as a personal failure. I spent many sleepless nights fixing bugs in third-party programs just so they could keep running on Windows 95. (Games were the worst. Often the game vendor didn't even care that their program didn't run on Windows 95!)