Well, how strongly you select for more flocculent yeast depends on how long you leave it in primary before harvesting. If you use short primaries, then you could potentially select for more flocculent yeast. But it would take many cycles before you would begin to notice a difference.
If the yeast was more flocculent, attenuation might suffer. But you could get around that by rousing the yeast frequently. I'm not sure how viable a plan that would be in a commercial brewery.
Top-cropping that way is a pretty common practice, at least in Europe. Not sure about the states. Some German breweries even do it with the thought that skimming of the kraeusen can help reduce off-flavors in the beer, though I'm not sure that's true. Maybe true of lagers, I doubt it's true of ales. It seem at any rate to be a good way to collect a consistent culture of yeast, but you need to be careful not to take enough to stall fermentation. So timing and quantity are important.