Not anymore it seems. I asked around before posting, since the last time I was on IB was 5 years ago. It seems that IB has improved tremendously.

I asked around a bit regarding CX and AMS and the move seems to be entirely motivated by pressure from TAs and shrinking loads on the AMS flights. Chinese, Taiwanese and Hong Kong tour groups to southern Europe are on the increase (+34% this year, after SARS though so figures distorted), a class of travellers that usually prefer Asian airlines over Western ones. Appearently CX can sell (group) tickets via AMS to MAD and BCN much cheaper than the LHR routing. CX wanted to fly HKG-ROM-MAD or HKG-CDG-MAD, but BA wouldn't have it. The IB code share seems to be a compromise.