I think it would be fair to say that eventually all these "foam" filter products will "decay" over time, whether it's genuine Poret, or a lesser known brand. I think the key to their longevity lies in how each hobbyist uses and treats their foam, and it seems to be pretty clear that we all have our different methods, hence different timescales regarding the foams degradation.
Using these foams as mechanical filtration where they're cleaned every week, scrubbed, beaten, dried out, basically manhandled to within an inch of their foamy lives, is entirely different to using these foams as bio media, where they may remain in situ for months on end. When they are eventually cleaned it is a very soft cleansing as not to eradicate the all important BB.
I think both these factors play an important role in the lifespan of these various foams. If anyone believes that their foams aren't lasting as long as they should, maybe take a look at your methods of usage and/or cleaning.