Who wrote 3.5

Ok let's have a look at the numbers. Here are the stats for AMD in particular...

3.5   : missing
3.4   : changesets 1.2% #19, lines 1.5% #15
3.3   : missing
3.2   : missing
3.1   : missing
3.0   : changesets 1.8% #12
2.6.39: changesets 1.3% #16
2.6.38: changesets 2.0% #9 , lines 1.1% #19
2.6.37: changesets 1.5% #14
2.6.36: changesets 1.4% #14
2.6.35: changesets 1.7% #10
2.6.34: changesets 1.3% #17, lines 1.5% #19
2.6.33: changesets 1.6% #13, lines 0.8% #18
2.6.32: changesets 2.3% #9
2.6.31: changesets 1.2% #13
2.6.30: changesets N/A, lines 2.1% #10

I'm afraid you mistook an exception for the rule. AMD had significant presence in all releases between 2.6.30 - 3.0, but then suddenly disappeared (apart from one exception that is 3.4).

(I created an index of LWN development statistics articles for easier reference here:
http://kernelnewbies.org/DevelopmentStatistics)