Wendy just published an interesting post on why architects are less litigious than other creators:

Are architects just nicer than other copyright holders? Unlikely.

More probably, they've found alternatives to the legal protections copyright gives. Like artists everywhere, they copy from the masters. They also have other ways of protecting their authorship interests: Architecture clients need full buildings designed, not just pictures of facades; architects can complain publicly about others who fail to give credit for inspiration, lowering the reputation of someone who copyright law might say has only used an unprotectible idea [see Ellickson]; and the great designers aren't just re-selling their last-years' designs in any event.