At the risk of being on the receiving end of some abuse, I think the Calendar Year Grand Slam could be more a nice thing for a player to say he has done rather than a serious achievement showing how good they are compared to other players. Tennis is not like sports such as football, where there are breaks of several months between seasons that allow teams to rebuild and regroup. Because football has clear breaks between seasons, going through a league undefeated and/or winning all of the trophies available is a genuinely significant achievement. In tennis, the only significant break between calendar years is December. As soon as the World Tour Finals and Davis Cup are out of the way, it's not that long before events like Brisbane and Doha come around. To me, it just seems arbitrary to set particular dates between which winning four grand slams is greatly more significant than winning four grand slams in a row over two calendar years. At the end of the day, the human body is not a machine and players hit form at different times of the year, which is not always on 1st January. The important thing is how long a player dominates, not the exact dates the domination began. For me, the only saving grace of the Calendar Grand Slam comes in the modern era. In part because of there being more surfaces on the tour now, but also because it could be argued that it's easier to win four slams on the bounce. If a player's run began with the US Open, it means he will have won two hard-court slams back to back and over a hard-court "season". This could be a fraction easier than having to win a hard-court slam, then a clay-court slam, then a grass-court slam and then returning to hard-courts.
NOW I AM TOTALLY CONFUSED AND LAUGHING OUT LOUD! One valid point you make is that it was probably easier for Laver and Budge to win their calender grand slams because 3 of them were on grass. In today's game winning the calender grand slam would be extremely difficult and more of an accomplishment than when Laver did it. But then, one could make arguments against this position too, NO DOUBT!