The difference is in the two diseases, I think. The problem with microglia in PD is that they don't turn off. In the study they were intentionally turned on and attacked the plaque. I use the analogy of teenage boys with nothing to do vs the same boys with a purpose:

"This is in contract to PD where the same cells when chronically activated have no plaques to target. Like a bunch of teenage rowdies unemployed and hanging out on the street corner, they degrade the whole neighborhood due to a lack of focus. Rumors of threats from surrounding neighborhoods keep tensions high even though they don’t materialize. Give them the needed focus, cleaning the junk off the local basketball court for example, and they improve things they would otherwise have degraded." More...