Ken if you go to one of your own hubs and then click on the 'suggest links' tab it will show you your current hubkarma. It still appears to exist although in this significantly more covert guise.
As to why the change - who knows, i certainly don't. Maybe Hub Karma did something bad in a previous cyber life :-) Lame but i couldn't resist, sorry.
I did come across plenty of hubbers that had no time for or interest in it or thought it made no sense to be linking off your own page and thus reducing the chances of people staying on your hub and thus potentially reducing the odds of having your own ads being clicked on.