yup - In fact I'd say in general one of the reasons that so few guys throw the curve anymore is that so many umps don't give the pitcher the whole K zone on a good curve.
The ump is probably right on these calls. A curve is falling rapidly as it crosses the plate. That fact that the catcher catches it below the box doesn't mean it's not a strike.
I get why he they don't want to give up on him - it's a big arm and he has a pretty good slider to go with the FB, but it's like the light just doesn't come on all the time.