George,
I noticed this as well, and found it very interesting. I doubt for a second people would have figured that Mark Omeara, Zach Johnson, and Sandy Lyle would all be in contention after day one. Tiger, Phil, and Vijay are also just a couple shots back. Each year it seems that past winners, some of whom never play well in any other PGA Tour events nowadays, find a way to sneak on the leaderboard at the Masters. Last year Ben Crenshaw played amazing and is a perfect example of this.
The reason for this, in my mind, has to be the golf course. Whether it was lengthened, trees were added, greens were faster, the fact that former champions always seem to find a way to creep on the leaderboard shows me how much of a strategic course Augusta really is. It showcases that there really are certain ways to play holes that former winners understand and the rest of the field not, hence the leaderboard and the low scores from past champions. Be it certain places to be in fairways, knowing when to play away from the hole and what part of the green to hit it to, or what club to hit off the tee, these past champions always seem to get it. That to me speaks volumes about Augusta, because it shows that after years of tinkering, it proves that strategizing around the golf course is the best way to go low.