Weird to me, someone who built desktops from 1989 (before Internet - remember the Computer Shopper huge magazine?) I find it very odd that reviews never mention how many slots are available. Dell was always skimpy, but nowadays it seems you're lucky if you have one free slot, and the GPU often blocks/covers it?
I think because USB is so fast nowadays that PCI slots aren't used? For example, try to get a FireWire port (old camcorders use it)...easiest way is an inexpensive PCI card. Apple sells a convertors cable, but it concerts to an older thunderbolt, so you need a 2ns cable to convert to USB / newer thunderbolt I believe.