It wasn't a stat comparison it was the fact that Crabtree getting hurt in SF basically caused people to write him off. Many said he no longer had it, but the Raiders gave him a shot and he made good on it.
But since you brought the stats up, lets look at them. The biggest reason Crabtree has far more production is because Britt got hurt in year 3 and it derailed his progress majorly. But since they entered the NFL together in 2009 it's easy to compare them. Over their first 2 season.
Crabtree's numbers: 27gms 103recs 1,366yds 8TDs
Britt's numbers: 28gms 84recs 1,476yds 12TDs
Not a huge difference in production there, Crabs was more of a possession guy while Britt was a downfield guy. It was year 3 that really separated them. Crab's numbers were on par to the previous 2 years 15gms 72rec, 874yds 4TDs, but Britt was poised for a huge breakout before getting hurt in week 3. 3gms 17rec, 289yds 3TDs. That season Britt was on pace for 90rec, 1,541yds 16TDs. Of course there's noway of knowing what exactly would have happened, but my point was that the Knee injuries, much like Perriman really hurt his development. But now he appears back and could be a great #2 for some team.