I concur, there is absolutely no difference between the D-Lux 4 and LX3 lens quality. Any differences seen in the IQ of the cameras was in the JPEG processing, shoot Raw and they are identical."The D-Lux 4 had a better lens than the LX3"......well we used to think that but comparing my DL4 to a friend's LX3 I can assure you that there is no difference.
Partly for that reason ( and the fact that I don't need Lightroom 3 and have given Leica quite enough this year for an X1 and accessories! ) I have acquired an LX5.
I look forward to hearing views of the DL5 lens.
I feel that the new lens just doesn't have quite the quality of the old..perhaps the price we pay for extra reach.