Hi Peter,
In recent years Hoover have dropped the use of beater bars, brought them back and then dropped them yet again. In addition they have also varied the density, length and stiffness of the bristles on the roller several times as well. Only reason I can think of behind this is that they are possibly trying to respond to changing trends in floor coverings, and adapting the design of their cleaners to suit.
Nowadays the "in" thing seems to be natural-looking carpets with a low pile, sometimes looped. This of course needs less aggressive agitation to clean successfully than the deep pile or sculptured carpets that were more popular a few years ago. Back when they were using beater bars, I do remember that Hoover upright cleaners carried the Axminster Carpets seal of approval, however I see no mention of this now.
I use a Kirby Ultimate G, which has a wooden agitator with no beater bars, just dense, stiff bristles arranged in staggered sections around the roller. Even without beaters it still manages to vibrate the carpet extremely well, and the amount of crap and sand it digs out of the pile is astonishing.