I've worked on both SaaS products and on-premise ones. While the challenges may be different, I was never at a loss for things to do in product management and product marketing. In fact, some of these tasks became more challenging, not less so, in a SaaS world.
Which makes me wonder, why on earth would someone who purports to be an expert on SaaS say that PM is not necessary in SaaS applications? To get my complete reaction to this recent post on SaaS University's house blog, click here.