People still going on about "a Gold is Gold no matter the event"? So if Federer had a Gold in Javelin he'd have a Golden Slam?
Of course it doesn't matter in terms of your success as an Olympic athlete or the pride in representing your country, but it's not at all the same thing when it comes to assessing a player's tennis career.
Like I said before: Phelps and Bolt are individual racers, they set up to be the best in the world and they win a lot in their own, they also put themselves for collective medals and those aren't less valid for their count.
Tennis doubles is still tennis, hell had Muzza lost the singles final and won the mixed doubles I'd still consider him an Olympic Champion, I do for Mirnyi, I do for Fernando González, for Rafa Nadal, for Marc Rosset, for the Woodies, etc