This is false. It supports PCIE 3.0, but doesn't require it. Cards that support PCIE 3.0 can be used in a 2.0 slot, which that motherboard has. Difference in performance wouldn't be noticeable in practical applications (you might see it benchmark a little lower in a 2.0 vs. a 3.0 slot).This is absolutely fascinating! I had no idea! I should read up about what the specifications for these expansion slots really mean. Absolutely good stuff to know.
Many connection standards in computers work this way. Newer hardware is often backwards-compatible with the older generations of their connection, where the tradeoff will be a slight limit i performance. You can still use USB 3.0 capable devices in a USB 2.0 port, but won't get max transfer speeds. You can connect a SATA III SSD into a SATA II port on the motherboard, but you'll get about half the advertised maximum read/write speeds on the SSD.
Works the same with PCIE 3.0, except that I don't think the power of most video cards is exceeding the capability of the PCIE 2.0 to enough of an extent to notice that you're not really getting the maximum performance from it. I would bet that the next generation of graphics cards might improve enough to where you'd really want a 3.0 slot to be getting the most out of the card. And by then, maybe PCIE 3.0 support will be far more common on motherboards as well.