Of course they're going to say that. They're also going to tell you that Facebook is yesterday and Twitter is taking over. (By the way, if anything qualifies as a short-term "fad" in my book, it's the flood of 140 character messages that are full of emoticons and abbreviations, but short on real content.)
For the longest time, PCs were cheaper than Macs. In fact, that was part of the reason why PCs won out over Macs in the years after Steve Jobs left Apple in the 80's.
Yet Macs still enjoy a strong presence in education, from grade school to college and post-grad. And they did even during the era when PCs gained big time.
I don't see how Chromebooks are going to be any different, if all they bring to the table is low cost.