Device missing from lspci on one linux distribution but not the other???!! How and Why?

Everything I've read says that when the Linux Kernel boots up, PCI devices are scanned and should be in /sys/bus/pci. I have two different Linux distributions, one shows a wireless device at 01:00.0, the other can't find it at all (not listed). The same driver is loaded on boot (ath5k). Under what circumstance would a device NOT show up even using lspci -M? Everybody I've talked to is convinced that can't be true, until I boot up on two different distress and literally SHOW them that on one it's there and the other, it's not. BTW, the two distributions in question are Antix (nothing shown) and MX (does show). Also Knoppix will show the device as well.