It seems to me that if they'd settled on the interdigitated profile, the launchers would have been configured to suit. This was the first generation, remember (perhaps even the "zeroth") - back-compatibility with previous models of the same missile would not have been an issue.
I could accept that a shift to an in-line profile might have made it easier for the rack designer to interface the various plug-ins with the missile internals, and the longer rack which the in-line profile allows might offer a more secure carry and stable launch, but it seems a little bit cart-before-horse to shape the missile's entire aerodynamic profile (and possibly more) around the launcher in this particular case. [/size]OTOH, A Sidewinder successor or competitor that was launched into an existing market, and constrained to use the same launcher, would be another matter.[size=78%]