Even were you to ask such a question in that manner to Borg, I'm still fairly certain he would rather win Wimbledon -- that was his dream coming up and the biggest tournament of the year for him. My point was, this fascination with winning on three surfaces is largely fan-driven, not player. Yes, once you're career is over it's nice to have a career slam and show that you have variety in your game -- however I don't know of any player that sets this as a goal, certainly not to do it within one year. Players want to be number 1, and win slams. Everything else is icing.
I will add one more thought after all, because I like what you said about players playing for titles and not surfaces.
BTW, I have no objection to continuing a friendly debate as long as a new point can be made. What I try to avoid is endless loops where two people are just repeating themselves constantly. FWIW, even if I don't completely agree on all your points, I fully understand your point of view. Even the points I might take issue with, I have no interest in changing your mind, so sometimes I just run out of things to say.
Back to my new comment...
I agree that players care about titles much more than surfaces. I think players want to be the FO champion, the Wimbledon champion, the AO champion, etc. Those events have traditions that matter to the players, although different players will certainly have their particular favorites.
However, you can't win Wimbledon without playing on grass. You can't win the French without playing on clay. You can't win the USO or AO without playing on hard court, at least not in quite a few years. The desire to hold those trophies is what makes the surface relevant, and it's the added difficulty of varying surfaces that makes some people take notice when a player can master them all. After all, not every great player was able to do that. We can make excuses all day long for why a certain player didn't, but I think it makes more sense to just celebrate those that did.
I asked myself to re-evaluate Nadal 2010 vs Fed 2006, and pretend all the surfaces were identical. I would still pick Nadal's year, but only because the AO probably has the least importance to me personally, of the 4 slams. If my least favorite was the FO, I would pick Fed's year instead. If I valued the YEC more than I do, I would pick Fed's year. If I valued win pct more than I do, I would pick Fed's year. There is simply no right or wrong answer as far as I'm concerned. I don't believe I have the right to tell anyone what they should
value. We're all free to make those choices for ourselves. I just try to explain how I arrived at my choice, for anyone that may be interested.