Making a custom field would be no harder than giving us all user titles. Mahz implemented those on the same day those were brought up. Chances are it's pretty much just copy-paste, and it's a single-time effort in any case. 
	There is no functional reason that I can think of here and now why [i]not[/i] to give users that tiny bit of additional customization, rather than having them clutter their bio/status/user title with info most others have elsewhere. Especially if their bio happens to be [i]huge[/i] and majority of individuals who glance at their profile might not read it. And so on and so forth. I've also seen plenty of people who [i]do[/i], indeed, consider "other"-option alienating. 
	So in the end, why argue against a pencil-in option? Sometimes, "But why not?" is the most telling question of them all. Since I can't think of any objective reasons, why not just give users 128 letters to say whatever they are in their own terminology and call it a day?