The court's decison turns around the mysterious language of 17 U.S.C. Section 204(a). Section 204(a) requires that a transfer of copyright be in writing, signed by the owner. The case law has not required a writing for a transfer of a non-exclusive license. I discuss non-exclusive licenses as a litigation defense at Section 13:12 of Copyright Litigation Handbook (3d Ed. West 2008).
The 9th Circuit had previously considered implied licenses in the context of movie special effects and architectural drawings. To illustrate: someone is paid $56,000 for special effects film footage, delivers it, then claims the film company can't use it. Effects Assocs. Inc. v. Cohen, 908 F.2d 555 (9th Cir. 1990) (link courtesy http://www.coolcopyright.com/). This is the "Moviemakers do lunch, not contracts" case.
But in this very hot area of work-for-hire disputes - the implied license doctrine has now been applied to software, substantially reducing the leverage that outside consultants may wield over clients who have not protected themselves in acquiring custom software.
An implied license may be found where (1) licensee requests creation of a work; (2) the creator makes the work and delivers it to the licensee who requested it; (3) the licensor intends that the licensee-requestor copy and distribute his work.
The AMS court found that Mister Computer intended, through "objective manifestations" that AMS "use, retain and modify" the software programs as well. Mister Computer should have put a better warning on his material. Now large and sophisticated software users, too, can do lunch, not contracts.