It's actually a somewhat serious explanation, even though I'd intended my previous post as a joke.
Since men can procreate with human women just fine, the appeal of asari to human women of a particular sexual persuasion is a bit more profound. For some women, mating with an asari would give them the chance of a child they wouldn't normally have.
The prospect of that is rather appealing. 
You don't even have to be "of a particular sexual persuasion" to find the concept appealing. There are women who would like to have kids that are theirs, but don't want to go through the pregnancy and childbirth process. Its more personal than adopting a kid, but a whole lot less trouble than giving birth to one.
As for Asari with boobs, there is prescedent for all-femal species who give birth without invervention right here on earth. From wiki:
Parthenogenesis is a form of asexual reproduction found in females, where growth and development of embryos occurs without fertilization by a male.
Modifié par Lady Nerevar, 23 avril 2011 - 02:28 .