Week one last season: 34-13 win against the Titans
Week two last seaosn: 20-18 loss against the Cardinals
While it's nice that you've at least come up to 24 points in two games rather than 20 points in 3 games, the numbers still are what they are.
2012:
-Wk1, at Ten (#21 pts, #29 yds): 13 pts allowed, 284 yds allowed
-Wk2, vs Ari (#31 pts, #32 yds): 20 pts allowed (7 came on a 2-yd score following a blocked punt), 242 yds allowed
-Wk3, at Bal (#10 pts, #16 yds): 31 pts allowed, 503 yds allowed
AVG: #20.7 pts, #25.7 yds: 21.3 pts allowed (19.0 if you don't count the 7 in the Arizona game against them), 343.0 yds allowed
2013:
-Wk1, at Buf (#20 pts, #14 yds): 21 pts allowed (7 were scored by the Bills' defense on a fumble recovery; so the D gave up 14 points), 286 yds allowed
-Wk2, vs NYJ (#28 pts, #30 yds): 10 pts allowed, 318 yds allowed
-Wk3, vs TB (#31 pts, #31 yds): 3 pts allowed, 323 yds allowed
AVG: #26.3 pts, #25 yds: 9.0 pts allowed, 309.0 yds allowed
The offenses they faced in the first three games of 2012 were a little better than what they've faced this year, but not a lot better. Somewhat better in pts scored ranking, but a little worse in yds gained ranking. But what the Pats' defense has done is significantly better than through three games in 2012.
So at this point, it's safe to say that the three-game sample in 2013 represents a much better performance than the first three games in 2012. Who knows what will happen from here on out. But so far, so good.