GLP & Unfair competition / another way of use

I just finished one well-written article by Till Jaeger named Enforcement of the GNU GPL in Germany and Europe. It is available for free on JIPITEC. What have drawn my attention is this paragraph.

Even companies that distribute GPL products without holding copyrights may soon begin to enforce the GPL by relying on unfair competition law (instead of copyright law) in order to obtain the complete corre-sponding source codes of improved software solutions from their  competitors.

It refers by means of the footnote to following literature.

See G. Spindler, Rechtsfragen bei open source, p. 128 and T. Jaeger/A. Metzger, Open Source Software, 2. ed, para. 336 et seq

Interesting thing to test in the court I would say. Last week I blogged on another intersection of unfair competition and GPL licensing (in Slovak) in regard to AVM v. Cybit case.