I agree 100% that it's opportunities, not Ryans, that's the issue. In 2006, Houston made 935 tackles (solo plus assist, so there may be some double counting in there). Of those, Ryans had 156, or 16.7%. This year, Houston has 99 solos + assists, of which Ryans has 15 for 15.2%. That's a little off, but then, as others have pointed out, the defense is better. He won't get a monopoly on tackles any more. All that said, 15.2% of 935 tackles is still 142.
Meanwhile, projecting those 99 tackles over a 16 game season gives 792--143 less than last year. Even at 16.7%, that means Ryans loses around 24 tackles on the season.
Bottom line: I think it's realistic to expect his numbers to take a bit of a hit this year, but that still leaves him as an elite lb.
P.S. I apologize for all the run-on stats--I took a shot of Nyquil in anticipation of my allergies driving me to bed early and I'm not sure I'm thinking too clearly!