This is a question that may not be for this specific thread - but regardless - could US Airways' actions be construed as being illegal if they start to purposely block seats? (What was the reaction of United's fan base when StarNet blocking began?)
Secondly, what are the chances that LH and US have come to an agreement that when a US customer tries to book a F ticket, they should be offered C instead? It's a real long shot based on two bits of anecdotal evidence but I hope others will respond as well to this... (FWIW, I have had on LH F redemption recently, and been offered several others when I was actually looking for LX on specific routings.)