The LED lights up whenever the Arduino has power. Two lines in a USB cable are 5v and GND, so any normal USB connection will give the Arduino adequate power. The remaining two lines are the problem.. those are the ones that pass data back and forth.
Not seeing any USB devices in the Network preferences pane says the OS hasn't loaded the driver necessary to handle that communication.
The Adruino IDE does use Java, but that works at a different layer of abstraction than the USB-communication part. I just downloaded a new Java runtime a couple days ago and have gotten the Arduino IDE to talk to several devices since then.
As for System Profiler, you may have seen the device without knowing how to identify it. I just connected an Uno to my Mac and it shows up in the USB report under the incredibly helpful name of 'Communication Device'.
It looks like your system didn't create an official 'device' when you plugged in your Arduino. I can't reproduce that on my own system, but try plugging in the Arduino you know to work, go to the Network pane again, and hit the '+' button on the bottom-left of the device list. That will give you the option to create a new device, and 'USB Modem' should (hopefully) be one of the options as long as the Arduino is visible to the USB controller.
When you void a product warranty, you give up your right to sue the manufacturer if something goes wrong and accept full responsibility for whatever happens next. And then you truly own the product.