As for the pressure differential issue, remember that air is dumb. It doesn't know it isn't supposed to creep up out of the house through a recessed "can" light stuck in the ceiling adjoining an attic. It just does. If the entire attic is in a negative pressure, and air has a choice to be made up from a can light or a gable end vent....there is no choice. Both will draw if a difference in pressure exists between the attic air space and an adjoining air space at a higher pressure. They won't move the same volume of air due to size, but both will move air. You don't really care if your gable end vent can ingest 200 feet per minute of air, but you should care your can light can suck air conditioned air from your house to provide air for the PAV.
Back to the first point...in my area, the window between needing heat and needing cooling is fairly small. We have a few weeks in spring and fall where the windows can be opened and the house ventilated/cooled naturally. The rest of the time we're either heating or cooling mechanically. In both cases, my efforts of late has been to help my house contain the air I pay to heat and cool. A PAV would countermand that effort. Going around and sealing the crap out of every penetration to the attic in my ceiling has not. The attic is ventilated naturally and has radiant barrier installed, so I expect our cooling load this summer to be managable. This will be our first summer in this house since buying it last fall, so we have no comparison to how it performed prior to these changes, but I expect it would be better.