It is graduated (as intended). The blurring available is so subtle it might appear to end suddenly, but if you put a desaturate at 100% on it you will see
Did anybody else notice that Lightroom 3 now allows you to blur images with adjustment brushes set to a negative sharpness? I was actually pretty excited to see this neglected new Gaussian blur effect. I searched the forums for something about this, but came up empty.
Before it was removed, I mentioned this a whole bunch of times in the beta forum.
Well, in B/W I still see the hard edge. It's right above the middle line, and it still doesn't look gradual. Although you did make a good point about it being stackable. The work-around would be to start with a -15 or so and the stack larger increments as it goes up.. but still not so smooth, and a bit of a bother.