QFileDialog doesn't list tty* files in /dev/ on Linux

I'm working on a Linux desktop application that needs to open a USB serial port, typically /dev/ttyUSB0 or /dev/ttyUSB1. I'm using QFileDialog to let the user select the file:

QFileDialog dialog(this);
dialog.setFileMode(QFileDialog::AnyFile);
dialog.setFilter(QDir::System | QDir::AllEntries | QDir::Hidden);
dialog.setViewMode(QFileDialog::Detail);
QStringList fileNames;
if (dialog.exec())
fileNames = dialog.selectedFiles();

When I direct the FileDialog to /dev, none of the files that I can see by typing "ls /dev -al" are there. The directories show up, but for example, this file doesn't:

luke@ThinkPad-W510:/$ ls /dev/ttyUSB0 -al
crw-rw---- 1 root dialout 188, 0 2011-10-11 10:14 /dev/ttyUSB0

My user is a member of the dialout group:

luke@ThinkPad-W510:/$ groups
luke adm dialout cdrom audio video plugdev users fuse netdev bluetooth lpadmin admin sambashare

I've tried adding QDir::Readable and QDir::Writable and the above file still doesn't show up.