Martin, IIRC you fly sparge. Is that correct? If so, have you tried batch sparging to see how it compares pH wise on the sparge?
I've only fly sparged in all my brews. (BTW, I finally passed the century mark with last week's brew. :-) It pales in comparison to Denny's 400+ batches, but I'm working on it).
I wouldn't think the pH results should differ between fly and batch sparging. The same volume of water is pushed through the grain bed and the same quantity of buffering from the malt is exhausted. Interesting question though.
I've found that if my mash pH is good, the pH through the sparge is almost always good with no water modification. I have fairly neutral water, though, so that undoubtedly has some bearing. If you decide to take the plunge into batch sparging a batch or 2, I'd be curious to hear what you find.