In reply to Display fonts vs text fonts- Arbitrary designations?:
Your samples may appear the same on screen only. A typical Display font is tweaked to have slightly thinner verticals, because it's intended to be used at larger sizes (this definition of "larger" is left to the type designer). So it's possible your screen just doesn't show the subtle changes.
Do the same exercise with a large point size and print it out on a high rez laser printer.
(There are some "Display" fonts that are not simply tweaked variants for larger sizes. The Display style of Aller Sans, for example, has quite a unique design of its own.)