I don’t think this is implied. The idea is probably that, like so many things, it’s on a spectrum and ‘asexual’ would describe one end of the spectrum. There is another end of the spectrum, but no one is saying everyone is on the outer end of it. But I must admit, I do somewhat share your sentiment, I’ve read lots of things by self-proclaimed asexuals in which I recognize myself, but I also think I have a quite average sexdrive. It makes me wonder if some people aren’t just a bit too eager to define themselves as different from the norm. I’m not talking about the further end of the spectrum, but there are those that really aren’t that different from your average person, but seem to want a box to fit in. Reading their description I would place them somewhere in the middle and still they describe themselves as asexual. Not that I care, go ahead, define yourself whatever way you want, if you want to think that you’re very different go ahead, it really doesn’t bother me, and who knows maybe you’re right, who am I to tell you you’re wrong?