King and I have been exchanging email offline about this issue, but just to bring other folks up to speed ...
Let's back up to color printing for a moment. If you print a color image to the Epson color driver (either called "Color" or "AccuPhoto HD") and let the application manage colors (e.g., "Photoshop Manages Colors") then you get identical output from CS3, CS4, LR 1, and LR 2, on Mac OS X Leopard. This is normal, desirable, and expected behavior. (Just to check, I have printed a target, measured it with an iSis, and the average difference between any pair of targets is ~0.15 DE 2000, with a max error of ~0.5 DE 2000.)
That's not the case for ABW, for some reason. In other words, if you keep everything above the same, but simply choose "ABW" mode in the Epson driver instead of the RGB color driver, you will get the same output from CS4 and LR1/LR2, but different output from CS3. Specifically, prints from CS4 & LR are much lighter than those from CS3. So, let's say you've printed a gray target to the ABW driver using "No Color Management" in CS3, then built an ICC profile to be used with the ABW driver based on that target. That profile works correctly with "Photoshop Manages Colors" in CS3. But it doesn't work with CS4/LR on Leopard.
Why is this? I don't know yet. But it's under investigation.