Angelo,
The current trend to fixed gear has absolutely nothing to do with a rule change. At the 2002 Nationals I witnessed large numbers of competitors in all classes flying retract equipped aircraft. I do believe a rule still exist to fly with the gear in the down position in the entry class Sportsman formerly known as Novice. Go to NSRCA.org judging and rules section for more details.
Having owned both a retract equipped and fixed gear equipped Hydeout I can honestly say there was not an appreciable flying difference between these two aircraft. The fixed gear version made grass field flying a no brainier and was less complex to construct and maintain.
http://www.geocities.com/rcprecision/nhof1.html (fixed)
http://www.geocities.com/rcprecision/hydeoutpic2.html (retract)
Glen
http://www.geocities.com/rcprecision/pah.html