I don't think this is such an accurate observation. The point system doesn't inflate, at all. Answers will not be getting 20+ rep a year (or two, or three) from now.
It's awesome to see questions answered in hours by people that earn 10+ rep on their answers.
People either have the intrinsic motivation to keep coming back, or they don't. Regardless of the reputation, or karma, or badges, that they can gain. Everybody participates at their own level.
People that do keep coming back, eventually earn more points.
Keep in mind that, more questions = more points (more answers = more points) in the system. But some questions/answers get deleted (when outdated) and the reputation is recalculated.